26 September 2006

Stubborn wave nearly a depression...

The easterly wave that left the African coast on Sept 18 is still intact, and has been on the threshold of being upgraded to a Depression for the past couple days.  It's had persistent deep convection, but no luck closing off a surface circulation.  There's a broad 1009mb Low associated with it, located at about 23N 50W.  It's in about 15kts of westerly wind shear, and over almost 28C water.  The next number/name on deck is 9/Isaac.

There's an impressive wave just exiting the African coast today at about 11N 19W which is quite interesting.  Otherwise, the basin is quiet.  As we head into October, the favored cyclogenesis locations are the western Caribbean and off the US east coast: http://www.nhc.noaa.gov/gifs/october.gif -- a sign of the "Cape Verde season" shutting down due to higher shear over the central and eastern parts of the basin.

2006 is on par with climatology so far, almost down to the day.  Using a 1944-2005 average, we typically have 7 named storms, 4 hurricanes, and 2 major hurricanes by this date, and we've actually had 8, 4, and 2.

Please visit my tropical Atlantic headquarters.

20 September 2006

Gordon and Helene both weakening...

Gordon passed over the Azores at 08Z this morning as a 65kt hurricane.  The strongest sustained wind reported at Santa Maria Island was 50kts, the lowest pressure reported was 990mb, and as of 15Z, the intensity was lowered to 50kts and 995mb.  It is holding onto its tropical characteristics, but is expected to gradually transition to extratropical as it passes north of Portugal and toward England over the next couple days.

Helene has weakened a bit to 90kts, and the satellite presentation is less than ideal.  The eye is no longer open, and cloud tops are not as cold as they have been.  The SSTs are ~28C, vertical shear is 10-15kts,  but there is a respectable amount of dry air to the southwest of the storm that could be entraining in.  The latest intensity estimate is 90kts and 958mb, moving NW at 10kts.  A gradual weakening trend is expected as SSTs decrease and shear increases.

The tropical wave I mentioned yesterday just off the African coast continues to get better organized.  Though convection is sparse and scattered, the low-level circulation is improving.  It's presently located at about 9N 29W, or approximately 600km SSW of the Cape Verdes.  This wave was generated over far eastern Africa on Sept 12-13, and has had a history of potent activity as it raced across the continent.  The next number/name on deck is 9/Isaac.

Please visit my tropical Atlantic headquarters.

19 September 2006

Gordon and Helene stirring up the central Atlantic...

Since my last update on Thursday, nothing new has formed, but Gordon has continued on a trip toward the Azores as a strong hurricane, intensity fluctuating between CAT1 and 3 (presently 90kts and 970mb).  It is heading directly for the Azores at 24kts and will hit them on Wednesday morning.  It has now been a hurricane for nearly 7 days.

Helene has intensified substantially since Thursday... it was upgraded to the 4th hurricane of the season on Saturday, and then the 2nd major hurricane on Monday morning, and still hanging on to that at 100kts and 960mb.  It too is safely out in the central Atlantic, no threat to the US, but the Azores may get another rough ride in about a week.

Elsewhere, there's a tropical wave near 25W that's presently not very convective.

Please visit my tropical Atlantic headquarters.

14 September 2006

Gordon strengthens, Helene forms...

At 03Z last night, Gordon was upgraded to 105kts, making it the first major hurricane of the season (CAT3+).  Twelve hours later, it's maintaining that 105kt intensity, with an MSLP of 955mb.  Just 24 hours ago, it was 80kts and 977mb, then 48 hours ago it was 50kts and 1000mb.  This didn't touch any rapid intensification records, but was still impressive.

The satellite presentation is spectacular: a large 40-mile-wide clear eye, symmetric convection, and few spiral rainbands.  However, things are about to change... looping the recent satellite imagery reveals an insurgence of westerly vertical wind shear, which will eventually reach a critical level and disrupt Gordon's major hurricane lifestyle.  Typically, once the shear is >20kts, the vertical coherence of the vortex is upset, and this is forecast to occur within the next 12 hours.  In about two days, it could already be weakened to a tropical storm.

It's forecast to maintain its current intensity for the next 6-12 hours, then gradually start weakening as it heads NNE-NE into cooler water and higher shear.

TD8 was upgraded to TS Helene, the 8th named storm of the season, at 03Z last night.  Although it's a VERY broad and diffuse surface circulation, the estimated intensity is 40kts and 1003mb.

It is predicted to remain over warm water with low to moderate shear, which should allow it to achieve an intensity similar to Gordon's within 4-5 days.  Again, the majority of models turn the storm more NW in 3-5 days, as the weakness in the subtropical ridge allows it to slip up that way (the same one responsible for steering Gordon into the north central Atlantic).

For those who keep tabs on the season's Net Tropical Cyclone Activity (NTC), 2006 is at 50.2% as of 15Z this morning, with the largest contribution coming from Gordon at 16.5%.  For comparison, we were at nearly 150% last year at this date.

Please visit my tropical Atlantic headquarters.

13 September 2006

Gordon rapidly intensifying...

The final advisory was written on Florence yesterday afternoon, as the extratropical transition raced to completion.  It was a named storm for almost 8 days.

Gordon was a 50kt TS (1000mb) yesterday morning, and just 24 hours later, is a 80kt hurricane with 977mb MSLP -- and this appears to be in the midst of a rapid intensification phase.  The storm is small, symmetric, has a beautiful open eye, and still in reasonable shear.  The SST is 29C, BUT the vertical shear is expected to pick up quite a bit in a day or so, so it has little time to strengthen.  It is forecast to move north through a weakness in the subtropical ridge.

TD8 is a large circulation, and has been slow to get better organized.  The forecast is for gradual intensification and a gradual curve to the NW over the next 5 days.  This solution is agreed upon by most models (not all).  Latest intensity estimate is 30kts and 1007mb, tracking W at 15kts.

Please visit my tropical Atlantic headquarters.

12 September 2006

Florence still a hurricane, Gordon and TD8 form...

Florence is now a minimal hurricane, and beginning an extratropical transition... still a warm-core cyclone, but the wind field is expanding, convection has departed the inner core, and it's becoming asymmetric.  The latest advisory has the intensity at 65kts and 982mb, and moving NE at 20kts.

At 21Z yesterday, TD7 was upgraded to TS Gordon, and it's now a 50kt storm, on the way to becoming the season's third hurricane.  Currently located near 23N 58W, it's forecast to more or less follow in Florence's footsteps and recurve to the north by 60W, safely to the east of Bermuda this time.  It should reach hurricane strength, but probably not have time for much more than that before increasing wind shear takes its toll.  Gordon is a compact storm, so in the near future, rapid intensity changes are not out of the question.

At 15Z today, the well-organized wave I mentioned immediately off the African coast was upgraded to TD8, just southeast of the Cape Islands at 12.5N 23W.  The satellite presentation is truly remarkable for a storm so far east, and the likelihood of it being upgraded to TS Helene later today is high.  The future should be just a general WNW track over the next 5+ days, with the potential for significant development.  The initial intensity is 25kts and 1007mb.  It's still close enough to land and a major field program that it will have some aircraft recon and dropsondes at this early phase of development... how exciting!  The vertical shear is forecast to remain VERY low over the next 5 days, with SSTs around 27.5-28.5C.
Coincidentally, this storm has a LOT in common already with Hugo '89 in terms of early genesis, African coastal exit location and date, etc.

Please visit my tropical Atlantic headquarters.

11 September 2006

Florence passes over Bermuda, TD7 forms...

Florence was upgraded to the second hurricane of the season early Sunday morning, about 500km away from Bermuda.  It passed very near the island with an intensity of 80kts and 972mb this morning.  Although still transmitting surface observations sporadically, the radar has been down since ~10Z.  As of this writing, the strongest gust has been 78kts, and sustained at 57kts...

TXKF 111555Z 21057G78KT 3SM -RA BR BKN008 BKN022 OVC120 26/25 A2914 RMK SLP867

This is more or less the end of Florence, and although it may maintain or even gain a little intensity over the next day or so, it will be due to baroclinic enhancement, and it is destined for an extratropical transition in about two days.  This is also the time it will be giving gale-force winds to Newfoundland.

The wave I was mentioning on Saturday to the southeast of Florence was upgraded to TD7 on Sunday night, and is now estimated at 30kts and 1009mb.  It's moving WNW at 8kts and is expected to be upgraded to TS Gordon later today.  The long-range track forecast indicates that it will slide north through the same weakness in the subtropical ridge that Florence did.

Elsewhere, a very well-organized tropical wave exited the African coast this morning after the trek across the continent since its origin 6 days ago over the Ethiopian Highlands.  The wave has an embedded 1008mb surface Low located near 12N 20W.  There's light shear over the system and warm SSTs, so this could quickly become TD8.

As you may recall, we had a strong hurricane off the northeast US coast on the memorable morning of September 11, 2001 (Erin), and that has happened several times since then, so I attached an collage of the four storms we've had on the mornings of other September 11ths, also not far from the coast, including today.

Please visit my tropical Atlantic headquarters.

09 September 2006

Florence nearly a hurricane, heading for Bermuda...

Since Friday afternoon, environmental conditions near Florence changed noticeably, and the storm was quick to notice.  Convection became deeper and more centralized, the dry air that was plaguing it seems to be absent, the vertical shear has dropped to around 10kts, and the SSTs are 29C+.  As of 15Z, the intensity was 60kts and 992mb.  A plane is /en route/ as I write this, and could very well find that it is now a hurricane.  Motion is NW at 11kts.

The forecast is for some substantial strengthening over the next two days, then quickly becoming extratropical and recurving into the north central Atlantic.  The official intensity forecast brings the storm up to 90kts over Bermuda, but they should be prepared for even worse, as rapid intensification is certainly possible today, tonight, and/or tomorrow given such ideal conditions.  Bermuda has a Hurricane Watch and Tropical Storm Warning, and a direct landfall is expected there early Monday morning as a CAT2 hurricane.  This is especially bad because it was only three years ago that the island was devastated by Hurricane Fabian.

There's also a wave behind Florence that bears watching, located at about 21N 50W... conditions are marginally favorable for development there.  The next name on deck is Gordon.

Please visit my tropical Atlantic headquarters.

07 September 2006

Florence slowly gaining strength...

It appears that Florence has been battling some mid-level dry air as well as moderate vertical shear, and as such, has been slow to reach hurricane intensity.  It's also a huge storm, and those are typically slower to intensify too.  The low-level center is completely exposed and there's even minimal convection elsewhere.  The intensity as of 15Z today is 45kts and 1000mb, position is 19.8N 53.4W, and motion is WNW at 7kts.

It is expected to recurve later this weekend, perhaps affecting Bermuda early next week.  It is also forecast to become a CAT2 hurricane by then, but given improved conditions, intensification beyond that is certainly possible.  Reaching the US is rather unlikely, thanks to a developing significant weakness in the subtropical ridge allowing it to slide north well offshore.  It only has 4 days to reach high intensity; after that, the SSTs and vertical shear become extremely detrimental.  Today, Friday, and Saturday however, all factors point to reaching at least CAT1 hurricane.

The strong tropical wave that was trailing Florence has more or less caught up to it and is being distorted/filamented by Florence's giant circulation.  A new wave exited the African coast today -- it was generated in eastern Africa back on Sept 2.

Please visit my tropical Atlantic headquarters.

05 September 2006

Florence forms in eastern Atlantic...

On Sunday afternoon, a strong tropical wave was upgraded to TD6, then further upgraded to the sixth named storm of the season, Florence, on Tuesday afternoon.  As of 21Z today, Florence was located at 17.4N 48.5W (roughly 1/2-way between Cape Verdes and Leewards) and tracking WNW at 10kts.  It's not very convectively active, but is forecast to gradually enter more favorable environmental conditions.   Satellite-estimated intensity is 35kts and 1005mb.

The longer-range forecast is very interesting -- a WNW track and possibly becoming the season's first major hurricane in a few days, yet still quite far from any land.

There is also a potent tropical wave on the heels of Florence, which exited Africa on Sept 1, just a couple days after pre-Florence did, and now located near 15N 35W.  This stands a pretty high chance of becoming the next depression/storm.  The next name/number on deck is 8/Gordon.  Florence and pre-Gordon (?) could also move close enough to each other to experience a Fujiwhara Effect... a well-known phenomenon involving interacting vortices in fluids.

Lastly, a brand new wave is introduced on the African coast today, after a very convective past few days over the continent... it was generated over the Ethiopian Highlands back on August 30 or so.  This also bears watching over the next few days -- we are in the prime of the Cape Verde season, so waves are climatologically favored to develop.

Please visit my tropical Atlantic headquarters.

31 August 2006

Ernesto getting ready for third landfall...

Ernesto made its way across Florida as a weak Tropical Storm and then Depression... then exited eastern FL near Cape Canaveral, and now heading NNE toward the SC/NC border.  It's also getting better organized each hour that it's over the ocean, and could be upgraded to a minimal hurricane by landfall late tonight.  The intensity as of 21Z today was 60kts and 991mb.

You can find an ever-growing radar loop of Ernesto's east coast approach at http://einstein.atmos.colostate.edu/~mcnoldy/tropics/ernesto06/Ernesto_31Aug06_LTX.gif
As of this writing, the center is due east of Georgetown SC, due south of Wilmington NC,  and heading NNE toward Cape Fear or perhaps Cape Lookout.  A Tropical Storm Warning is in effect for all of SC and NC, and a Hurricane Watch is in effect for northern SC and southern NC up to Cape Lookout

Across the rest of the basin, there is an impressive tropical wave near 11N 25W which certainly bears watching over the coming days.  Another circulation can be found about 10 degrees west of that, and also has a shot at development, but the one to the east looks healthier now (better divergence aloft, less shear).  The next names on deck are Florence and Gordon. 

And of course, http://mcwar.org/tropics/ has the latest satellite imagery, track forecast, and more for the basin.

I'd also like to welcome several new additions to the mailing list, 6 in the past week alone!  That brings the total up to about 310 subscribers... homeowners, students, teachers, media, military, enthusiasts, business owners, and more.  I'm reminded of and humbled by the large number of people who've opted to subscribe to these updates!  This is year #11 for them...

Please visit my tropical Atlantic headquarters.

29 August 2006

Ernesto heading for Florida...

The center of Ernesto's circulation finally exited north central Cuba at 06Z this morning (2am EDT).  Deep convection has been somewhat sparse and slow to come back, but it is gradually increasing in coverage as more of the storm arrives over the ocean.  The ocean is at least 26C down to a depth of 80m in the Florida Straight, and the SST is a tad over 30C, so there's no shortage of energy for the storm, just a shortage of time.

You can track the progress of the storm via Miami's long-range radar at: http://einstein.atmos.colostate.edu/~mcnoldy/tropics/ernesto06/Ernesto_29Aug06.gif
(updating loop, new frame added every 6 minutes or so, beginning at 12Z this morning)

At 15Z this morning, the tropical storm was located at 23.3N 79.5W and tracking NW at 11kts.  It only has a generous 24 hours over ocean before hitting the southern tip of the FL peninsula, so at this point, intensification to a hurricane seems very unlikely (it's at 40kts and 1005mb now).  As of the latest official forecast, the Keys are in the center of the track "cone", but for a storm without an eye, that doesn't matter so much -- all of southern FL will experience stormy weather beginning today and going into tomorrow.  Threats of inland flooding and tornadoes are the highest.

After making its way northward across FL, the forecast takes it up into SC, around Charleston, again as a strong Tropical Storm (a minimal hurricane isn't out of the question).

A tropical wave that exited Africa on Sunday is now located at about 12N 29W.  It's moving west, and the environment is favorable for slow development.

And last but not least, this morning is the one-year anniversary of Katrina's landfall on Mississippi and Louisiana... and although not the strongest or deadliest landfall, it was the costliest disaster in US history, by far.  You can view the radar-based view of that fateful landfall at http://einstein.atmos.colostate.edu/~mcnoldy/tropics/katrina/Katrina_29Aug05.gif

Please visit my tropical Atlantic headquarters.

28 August 2006

Ernesto over Cuba...

Debby finally dissipated on Sunday afternoon as an insignificant low-level swirl in the north central Atlantic, now pretty much absorbed by a mid-latitude trough.

Ernesto is still the big story in the basin.  The long-range track forecasts from the middle of last week have proven to be very wrong, and the storm has tracked NW instead of W-WNW.  So, in this scenario, everyone loses: the storm is scraping over Cuba, which is bad for Cuba and bad for the storm!   A Hurricane Watch is in effect for all of southern Florida and the northern Bahamas, and a Tropical Storm Warning is in effect for eastern Cuba and the central Bahamas. 

As of 15Z, the intensity is 35kts and 1003mb, barely a tropical storm, but it's also tracking directly over mountainous eastern Cuba.

Once Ernesto leaves Cuba late tonight or early tomorrow morning, it should have a short but critical stay over the ocean before a Florida landfall late Tuesday night.  The SSTs will be around 30C and vertical shear 10kts or less, so the trip between Cuba and Florida could allow for rapid intensification.  You can keep an eye on the approach via Miami's radar:
This is an extraordinarily challenging forecast, because it's approaching the Florida peninsula from the south.  A SLIGHT east-west error in track forecast could mean landfall in Apalachicola, Key West, Miami, Charleston, or Wilmington!  This angle of approach is sensitive to the smallest track deviations.  Miami is presently in the center of the target.

As of right now, the official forecast has the storm scraping eastern FL, crossing over the Gulf Stream, then making a 3rd landfall on North Carolina as a strong hurricane too.  This is something that clearly should be watched closely by east coast residents.

Elsewhere, there is a significant tropical wave with an embedded 1010mb Low located at about 17N 40W.

Please visit my tropical Atlantic headquarters.

impending disaster, exactly 1 year ago today...

This is just something to reflect back on, one year to the day of an impending major natural disaster.  On the morning of August 28, 2005, a day prior to Katrina's landfall on Mississippi, the New Orleans National Weather Service Office tried to make it clear that a total evacuation was essential (for those who still remained behind).  The events that would unfold were told in countless documentaries for a decade or more prior to the Katrina's landfall, owing to the human-engineered disaster-waiting-to-happen.  It happened, and with predictable and nightmarish results.

1011 AM CDT SUN AUG 28 2005









Please visit my tropical Atlantic headquarters.

27 August 2006

Debby dissipating, Ernesto now a hurricane...

Debby has been slowly decaying, and is now a convectionless 25kt vortex with a 1012mb MSLP.  It's heading north into the extratropical realm of the north central Atlantic.  Strong vertical shear has overwhelmed moderate SSTs.  By Monday-Tuesday, Debby will have lost its identity as it's absorbed by a mid-latitude front.

Ernesto was upgraded to a hurricane on Sunday morning... the first hurricane of the Atlantic season!  As of this writing, it is located on the far western tip of Haiti, heading for Jamaica later today.  Intensity is 65kts and 997mb and motion is NW at 8kts.  Microwave imagery from earlier this morning revealed what appears to be either a very tightly-wound spiral band or the embryonic stages of eyewall development.

The deep-layer shear (850-200mb) has relaxed immensely, thanks to a maturing anticyclone sitting directly over the low-mid-level cyclone.  Now that those ingredients are aligned, further intensification will occur more readily -- also, oceanic heat content along the projected track of Ernesto is astronomical... VERY deep warm water will provide a boundless source of energy.  The only thing hindering explosive development is land interaction (Jamiaca, Cuba), which should put a brake on rapid intensification.  By Tuesday morning however, Ernesto will have cleared Cuba and entered the Gulf of Mexico, potentially poised for rapid development as it heads toward the US coast.

As of now, the forecast track takes it into Tampa, FL on Thursday morning as a strong hurricane.
A Hurricane Watch is in effect for Jamaica and the Cayman Islands... and a Hurricane Warning is in effect for southern Haiti and eastern Cuba.  A Hurricane Watch/Warning maybe added for western Florida and western Cuba later today.

Please visit my tropical Atlantic headquarters.

25 August 2006

Debby weakens, Ernesto forms...

Debby is having a hard time maintaining deep convection in the face of 25kt shear.  The SST is 28C, but that warm water is quite shallow there too.  It's located at 23.9N 43.3W and tracking NW at 15kts now, with a satellite-estimated intensity of 35kts and 1003mb... barely holding onto tropical storm status.  The forecast is unchanged: fluctuate a bit in intensity and recurve by 55W.

At 21Z yesterday, the strong tropical wave near the Lesser Antilles was upgraded to TD5 based on an aircraft flight into it.  Today at 21Z, it was further upgraded to TS Ernesto, again based on aircraft recon.  The storm is experiencing decent westerly vertical wind shear, so the low-level center is displaced to the west from the deep convection.  Recall that this wave was born in the Ethiopian Highlands way back on August 10 or so, and exited Africa on August 17.

At 19Z today, Ernesto was located at 14.1N 67.3W.  The intensity is 40kts and 1004mb... this may be adjusted slightly for the official 21Z advisory.

The forecast for Ernesto is very interesting, particularly for the Gulf coast.  Over the next couple of days, it is expected to maintain its WNW heading and somewhat formidable shear, but after that, it enters lower shear, and VERY high oceanic heat content in the western Caribbean.  In 5 days, it should pass between Yucatan and Cuba, heading in to the Gulf of Mexico as a possibly powerful hurricane.  There is too much uncertainly beyond 5 days, but once in the Gulf, it HAS to hit somewhere.

Elsewhere, a new potent tropical wave is introduced off the African coast around 18W with an embedded 1008mb Low.  We're now entering the heart of the "Cape Verde season", so these all need to be watched closely.

Also, today is the 1-year anniversary of Hurricane Katrina's Florida landfall.

Please visit my tropical Atlantic headquarters.

24 August 2006

Debby struggling...

Debby is presently experiencing the coldest SSTs of its journey thus far, around 26C.  There is only minimal convection associated with the storm now, and it looks rather ragged.  Over the next few days, the SSTs will increase again (up to almost 29C), likely allowing the storm to reintensify, and PERHAPS finally reach hurricane status.

skip this part if you're just interested in the headlines...
The SST is an important ingredient in intensity forecasting, but far from the only one.  From a strictly thermodynamic viewpoint (disregarding shear, eyewall replacements, land, dry air entrainment, boundary layer humidity, other moisture-related issues), the outflow temperature is just as important.  If you assume the outflow of the hurricane to be at about 200mb, you can use the temperature there and find the difference between that and the temperature at the inflow layer (sea surface).  It's this difference that controls the lapse rate and instability in the hurricane near-environment.  Using Debby as an example (and taking the diagnosed SST along the forecast track from a statistical model called SHIPS), we get the following:
-- Thursday morning SST: 26.1C
-- Thursday morning outflow temp: -53.0C
-- Thursday morning's DIFFERENCE: 79.1C
-- Saturday morning SST: 28.5C
-- Saturday morning outflow temp: -54.1C
-- Saturday morning's DIFFERENCE: 82.6C
So, in a couple days, the temperature difference between the inflow and outflow of the storm will be 3.5C greater, which in the tropics is a big deal, because lapse rates typically vary VERY little there.  Taking this morning's data and tweaking it a little just to make a point, suppose the outflow temperature were -56.5C... you'd get exactly the same healthy lapse rate as what is forecast for Saturday morning!  In the tropics however, SSTs are of more interest because the outflow temperature typically changes so little.  There are subtleties involved with this explanation, but that's the basics!

The latest intensity estimate (15Z) for Debby is 45kts and 1000mb, and heading WNW at 17kts.  It is located at 20.4N 37.8W, basically in the middle of the basin, and heading for even more open ocean.  It is forecast to slowly strengthen as it turns to the NW then N, recurving by 55W.

The strong tropical wave that was near 11N 55W yesterday is near 12N 61W today, and not organized enough to be upgraded to a tropical depression, but it is still convectively active and showing signs of at least a mid-level circulation, if not low-level as well.  It's tracking W at 15kts and has a 1009mb Low embedded within it.  This could be upgraded to TD5 or TS Ernesto within the next 24 hours, and in the long run, stands a very good chance at reaching hurricane intensity as it cruises through the central and western Caribbean -- low shear, 30C SSTs, and significant oceanic heat content!

Please visit my tropical Atlantic headquarters.

23 August 2006

TD4 upgraded to TS Debby...

At 03Z today (Tuesday night in the US), TD4 was upgraded to the forth named storm of the season, Debby.  This was based on infrared and microwave satellite imagery.  As of 15Z, the intensity estimate is 45kts and 1000mb.  It's located about 5 degrees due west of the Cape Verde islands.

The forecast for Debby is gradual strengthening, possibly reaching minimal hurricane intensity during the weekend.  The track should follow a WNW to NW course, which will momentarily take the storm over cool water (25C), but in about 3 days, will be back over 28-29C water.  However, combating that increase in SST is an anticipated increase in southwesterly vertical wind shear.

Elsewhere, the tropical wave that was near 50W yesterday is still lacking an organized low-level circulation, but the mid-level circulation is located at about 11N 55W and tracking W at 15kts.  It has been convectively active in bursts, and chances of formation seem fairly high by the end of the week.  This is the wave that exited Africa back on August 17.  If this develops, the forecast would be for a WNW track through the heart of the Caribbean, likely becoming at least a tropical storm, if not a hurricane.  The next number/name on deck is 5/Ernesto.

Please visit my tropical Atlantic headquarters.

22 August 2006

TD4 still organizing...

Based on infrared satellite presentation and a QuikSCAT pass (active microwave scatterometer that can measure surface winds over water), TD4 has been held at Depression status as of 15Z today.  It is definitely on the threshold of being named though.  The latest intensity estimate is 30kts and 1007mb.

The most recent visible satellite imagery as of this writing shows deep convection over the low-level center, rather well consolidated.  There's healthy outflow everywhere, but moreso to the south, as was the case yesterday.  Two negatives for it are stable air to the west and north, and slight southeasterly vertical shear.  It's tracking WNW at 14kts, and is located just southwest of the Cape Verde Islands. 

It's still forecast to gradually intensify and track WNW for a few more days, then recurve northward through an anticipated weakness in the subtropical ridge.

Elsewhere, there are two points of interest, one in the central part of the basin, near 50W, and one still over the heart of Africa, at about 5W.  The one still over Africa obviously has a few days before it even hits the ocean, but it looks ominous.  And the one nearing the Lesser Antilles is definitely worth keeping an eye on.  In fact, there's a broad elongated envelope of enhanced cyclonic vorticity from about 45-60W along ~12N, and there appears to be at least two embedded mid-level circulations.

Please visit my tropical Atlantic headquarters.

21 August 2006

Tropical Depression 4 forms in the far eastern Atlantic...

A very strong African Easterly Wave born in far eastern Africa back on August 14 exited the coast Sunday afternoon.  It quickly acquired a mid-level circulation and later on Monday developed a low-level circulation as well, prompting the upgrade to TD4.  As of this writing, it has deep convection in large spiral bands, but not too concentrated yet over the center... divergence aloft is healthy, with a stronger outflow channel to its south.

The 21Z advisory places the center at 12.3N 21.0W, or just south of the Cape Verde Islands.  The satellite-estimated intensity is 30kts and 1007mb.  Motion is toward the WNW at 11kts.

It is forecast to slowly intensify and track NW through a weakness in the subtropical ridge.  It seems unlikely as of now that this will be the type to travel the full distance across the basin before recurving.  The next name on deck is Debby.

Please visit my tropical Atlantic headquarters.

09 August 2006

Possible Depression forming...

The tropical wave I had been mentioning since LAST Wednesday has finally entered a more favorable environment (the problem was primarily dry, stable air surrounding it) and has been sporting a cold CDO for the past 12-18 hours.  However, a recent aircraft flight into the system was unable to find a closed circulation, so for now, it remains a strong tropical wave.  There is decidedly a closed mid-level circulation though.  It is located over Barbados and tracking W at 15kts.  I was perusing a series of soundings from Barbados over the past 48 hours, and the precipitable water increased from 4.34cm to 5.56cm in that time... a likely sign that whatever Saharan Air Layer was present has since weakened/dispersed.

Forecast models take it WNW into the western Caribbean over the next 5 days.  Statistical models intensify it to at least a minimal hurricane, while the dynamical models don't even bring it up to a TS.  This will be an interesting "competition"!  If it develops, it would be TD4 or TS Debby.

The other two easterly waves at 38W and 86W are not of great concern right now; they suffer from dry air and high shear, respectively.

Please visit my tropical Atlantic headquarters.

07 August 2006

Chris dissipates, TD4 on the horizon?...

TD Chris never did regenerate, and dissipated early Saturday morning
near the northern Cuba coast.  The remnants, an open easterly wave, can
still be found in the central Gulf of Mexico.

The potent easterly wave that I first mentioned last Wednesday has
continued its trek across the basin.  It formed over the Ethiopian
Highlands around July 26, exited Africa on August 2, and is now about
1500km east of the Windward Islands.  It has a very well-defined surface
circulation, but is lacking deep convection (though the trend of that
has been upward the past few hours).  Environmental conditions appear
quite favorable for further development, and this will likely become TD4
later today or tonight.  The embedded Low has a pressure of about
1009mb, and is located at approximately 12.5N 43.0W, tracking W at
15kts.  Forecast models take it WNW toward the Leeward Islands and
Hispaniola over the next 5 days, and intensify it to a strong TS or
minimal hurricane.

Another healthy wave has just exited the African coast on Sunday and is
presently at about 24W.

There is a convectively-active tropical wave also located at about 70W,
but shows no signs of circulation.

Please visit my tropical Atlantic headquarters.

04 August 2006

Chris weakens to a Depression...

Deep convection has failed to regenerate over the center of Chris, and in the face of persistent strong vertical shear, the system was downgraded this morning to a Depression.  It's currently a poorly defined low-level swirl over the Turk Islands.  The surface circulation is generating heavy rain over Hispaniola to the south.

The majority of forecast models take Chris westward over the next 5 days, ending up in southern TX or northern Mexico.  Some track it over Cuba, some track it over the Florida Straight, which will make a huge difference in intensity.  The 5-day intensity forecasts vary from minimal TS to minimal hurricane, and the official forecast calls for 45kts in 5 days.  The hefty vertical shear lately is due to a tag-team effort of two upper-level Lows... once Chris passes by them, a large ridge centered over the eastern US should shelter the storm and steer it due west.
SSTs in the Gulf are 29-30C, so that will not be a problem: http://einstein.atmos.colostate.edu/~mcnoldy/tropics/sectors/sst/gulf15.php

Elsewhere, the two previously-mentioned easterly waves are still tracking across the basin at about 15kts... they are presently at about 48W and 22W.

Please visit my tropical Atlantic headquarters.

03 August 2006

Chris abruptly weakens...

Wednesday was characterized by intense deep convection, even up through early evening.  Then, toward the end of the day and throughout the night, the system was attacked by increased northerly vertical shear and very dry low-mid level air, choking off and stripping off all convection.  As of this morning, all that remains is a shallow surface circulation, roughly north of eastern Dominican Republic.  The latest intensity is 35kts and 1012mb.

You can still find a running radar loop of Chris at http://einstein.atmos.colostate.edu/~mcnoldy/tropics/chris06/Chris_02Aug06.gif ... it begins Wednesday morning and is still being added to.  Parental notice: the loop contains a violent dismemberment, only intended for mature audiences (rated TC 13).

Chris is barely holding onto TS status, and is forecast to degenerate into a Depression shortly.  Although the official forecast holds the system at 30kts for the next 5 days, it is certainly not out of the realm of possibilities that environmental conditions will improve, and this low-level vortex over steamy SSTs will take advantage of it.  The steering flow will remain toward the WNW at 10kts.  This will still take Chris, at whatever intensity, near the Florida Straight and into the Gulf over the next 5 days.

There are two other areas of interest in the basin: both African Easterly Waves.  One is at 43W, the other at about 19W.  Both of these will be monitored for development, as the classic "Cape Verde season" picks up.  The next names on the list are Debby and Ernesto.

Please visit my tropical Atlantic headquarters.

02 August 2006

Chris strengthens further...

Beginning Tuesday late afternoon, deep convection began firing closer to the center of Chris, accompanied by much more impressive aircraft data (increasing flight-level winds, noticeable pressure falls).  This continued throughout the night, and today TS Chris is sporting a classic CDO (Central Dense Overcast) with cloud tops around -75C, and evidence of northerly wind shear... decreasing with time.  Chris is a small storm, and as such, will be easily influenced by shear, but conversely, will be quick to bounce back.  SSTs under and ahead of the storm are a cozy 28C.

At 15Z today, TS Chris was located at 19.2N 63.4W, or just north of Anguilla in the northern Leeward Islands.  It is heading WNW at 9kts, and the latest intensity is 55kts and 1001mb.  A Tropical Storm Warning is in effect for Puerto Rico and the Virgin Islands... a Hurricane Watch is in effect for the western islands of the Bahamas.  You can monitor the progress of the storm via radar in San Juan at http://radar.weather.gov/radar.php?rid=JUA&product=N0Z&overlay=11101111&loop=yes

Over the next few days, it is expected to gradually strengthen to a hurricane, and continue a WNW heading, bringing it over the Bahamas on Saturday morning, and passing very close to southern Florida on Monday morning.  The forecast track optimizes its stay over warm water and away from mountainous islands, allowing for the most intensification.

In the longer range, the central Gulf coast should be watching Chris with great interest.  Once the storm passes over or near southern Florida on Sunday, the storm will enter the Gulf of Mexico.  As of now, it appears that LA and TX would be the higher risks.

Elsewhere, a potent tropical wave just exited the African coast today.  It had its earliest origins in the Ethiopian Highlands about a week ago and is favored by computer models to develop and become quite strong.  The next name on deck is Debby.

Please visit my tropical Atlantic headquarters.

01 August 2006

Chris forms near Leeward Islands...

Back on July 24, a tropical wave left the African coast.  At 03Z today, that vigorous wave was upgraded to TD3 based on buoy and satellite data.  Although initially fairly disorganized, vertical wind shear has relaxed and the Depression was further upgraded to the third named storm of the season, Tropical Storm Chris, at 09Z today.  It is still not well-organized -- the center is hard to find and the deep convection is scattered.

It is located just east of the islands of Barbuda and Antigua in the Leeward Island chain and heading for them, moving WNW at 9kts.  The latest intensity estimate (15Z) is 35kts and 1009mb.  Tropical Storm Warnings and Watches cover the northern Leeward Islands and Puerto Rico, respectively.

The forecast is for continued strengthening over the next several days, and the track should take it over the Virgin Islands, north of Puerto Rico, Hispaniola, and Cuba, and through the Bahamas.  It presently appears that the southeast coast of Florida will want to monitor this storm very closely, as it could affect the state by Sunday as at least a strong TS.

Please visit my tropical Atlantic headquarters.

20 July 2006

Beryl brushes US east coast...

On Tuesday morning, an area of disturbed weather off the North Carolina coast was upgraded to TD2 based on buoy reports, visible satellite, and microwave satellite imagery.  It has since drifted slowly northward along the coast, intensified slightly, as was further upgraded to TS Beryl.  It's presently off the New Jersey coast (early Thursday afternoon), heading NNE, and gradually weakening in the face of ever-cooling sea surface temperatures.  The latest intensity is 50kts and 1002mb.

An approaching trough to the west of Beryl will allow for baroclinically-enhanced rainfall to the north of the tropical system, including all of New England.  A Tropical Storm Watch covers eastern Long Island, RI, and CT.  A Tropical Storm Warning is in effect for eastern MA.  Between the approaching front and tropical storm, the northeast US can expect to be quite wet in the next 1-3 days, with the potential for several inches of rainfall from PA on up to ME.

Elsewhere, although the basin is typically quiescent in July, it is extraordinarily DEAD right now.  There's an easterly wave nearing the Bahamas, but it's convectively inactive at the moment.

Please visit my tropical Atlantic headquarters.

13 June 2006

Alberto makes landfall...

At around 16Z today, Alberto came ashore near Dekle Beach, FL as a 45kt tropical storm.  The MSLP was 996mb -- coastal locations to the east of the landfall point are experiencing 5-7' storm surges due to the shape and bathymetry of this portion of Florida (very easy to get big surges).
You can view a radar loop of the entire approach and landfall at
Of note is the burst of deep convection near the circulation center as it comes inland, indicating enhanced frictional inflow.  This is a fairly common, though ephemeral, last gasp of a tropical cyclone.

So far, 4 tornadoes have been reported in association with Alberto, and that threat remains high today in northern FL and eastern GA and SC.  The other significant threat is flash flooding.  It is forecast to zip off to the northeast as it merges with a mid-latitude trough, losing tropical characteristics as it does so.

Elsewhere, an easterly wave that exited the African coast on June 7 is now located near the Windward Islands.  It's been moving west at 15kts and still disorganized, but will be watched!  There is also a wave exiting Africa today, which had its root in the Ethiopian Highlands back on June 7.  You can track waves' progress across the tropical Atlantic and Africa at http://einstein.atmos.colostate.edu/~mcnoldy/tropics/hovmoller/atlantic/

Please visit my tropical Atlantic headquarters.

12 June 2006

Alberto heads for the Florida coast and strengthens...

Alberto has recently intensified quite notably, and now has sustained winds of 60kts and a central pressure of 997mb.  It is forecast to briefly achieve minimal hurricane status prior to landfall.  The forecast track is centered on Piney Point, west of Gainesville, but keep in mind forecast uncertainty... anyone from Tampa to Apalachicola should be prepared for severe tropical weather, which includes strong winds, flash floods, storm surge, and tornadoes.

The storm has slowed down a bit, and landfall isn't expected until Tuesday afternoon now.  This slower motion increases intensification potential, HOWEVER, the oceanic heat content will be lower and vertical shear should be higher, so the net effect might be maintaining intensity or minimal strengthening.

At 15Z today, TS Alberto is located at 27.1N 85.9W and crawling NNE at 6kts.  This puts it 220 miles southwest of Cedar Key, FL and about 36 hours from landfall.
Alberto's circulation is visible from Tampa's radar:
and will be from Tallahassee's radar later today:

Hurricane Warnings and Tropical Storm Warnings are now in effect for much of western Florida -- please visit http://www.nhc.noaa.gov/refresh/graphics_at1+shtml/144536.shtml?3day for the latest warnings.  The biggest threats from this landfall will be storm surge and tornadoes in the spiral rainbands.  Tornadoes have already been reported in western FL, and it's still 36 hours from landfall.

Please visit my tropical Atlantic headquarters.

11 June 2006

TD1 upgraded to TS Alberto...

At 15Z today, the season's first named storm formed in the southern Gulf of Mexico, Tropical Storm Alberto.  This upgrade was based on an aircraft recon flight into the storm this morning and a nearby ship report.  An active microwave scatterometer also observed 35-40kt surface winds on the north and east quadrants of the storm center.  Alberto is located at 23.9N 88.1W,  and tracking NW at 8kts.  Measured intensity is 40kts and 1004mb, and is narrowly holding onto TS status.

The satellite presentation is not as impressive today, as the entire bulk of deep convection is located east of the low-level center, indicating respectable westerly wind shear. However, there is a strong rain band on the east side, and a weaker one to its east that is already making its presence felt in the western FL peninsula.  SSTs are around 28C, and the storm is passing over the Loop Current in the Gulf, which means slightly higher SSTs and noticeably higher heat content during the next day or so.

The NW motion should soon become more northerly, then northeasterly by Monday morning.  It is still expected to make landfall north of Tampa late Monday night as a moderate TS.  Computer model guidance is fairly consistent with the track... practically all solutions lie between Tampa and Tallassee.

Please visit my tropical Atlantic headquarters.

10 June 2006

Tropical Depression 1 forms in the northwest Caribbean...

After over a week of crawling and festering, an area of disturbed weather in the western Caribbean finally developed a closed surface circulation, and was upgraded to TD1 at 13Z today.  It has a very impressive satellite presentation, and is nearly a Tropical Storm.  There is a very robust and cold CDO, or Central Dense Overcast, a sign of healthy intensification seen in the early stages of development.

At 13Z, TD1 was located at 21.1N 85.3W and moving NNW at 10kts.  Maximum sustained winds are 30kts and the minimum sea level pressure (MSLP) is 1003mb.  It is expected to strengthen to a TS later today as it heads into the southern Gulf of Mexico.  If this intensifies to 35kts, it will be upgraded to Tropical Storm Alberto, the first named storm of the season (as an aside, the first named storm of 2005 formed on June 8).  Tropical Storm Warnings are in effect for western Cuba.  The forecast track will also make this our first landfalling storm of the year too, probably north of Tampa, FL late Monday night (the first named storm of 2005 made landfall on the FL/AL border on June 11 as a 50kt TS).  After crossing the FL peninsula, it's predicted to travel northeast along the east coast of the US as it speeds up and merges with a mid-latitude trough.

Please visit my tropical Atlantic headquarters.

04 April 2006

2005 Atlantic Best Track

The NHC has just completed their "Best Track" reanalysis of the 2005 Atlantic hurricane season.  This allows the forecasters and hurricane specialists to look at the storms in hindsight and evaluate with an objective eye the track and intensity.  This often changes the numbers a bit, but they more accurately reflect what happened, which is not always the case in the hurried operational timeframe.
You can find the individual storm summaries at: http://www.nhc.noaa.gov/2005atlan.shtml

So, we ended up with 27 Tropical Storms, 15 Hurricanes, and 7 Major Hurricanes.  Amazingly, 4 of those major hurricanes were Category 5s.  These huge numbers, combined with the cumulative longevity of them, produced a season that was 276% of an "average" season (this is the NTC or Net Tropical Cyclone activity).

Storm with most time spent at 35kts+: Ophelia (10.75 days)
Storm with most time spent at 65kts+: Wilma (7.50 days)
Storm with most time spent at 100kts+: Wilma (4.75 days)

Contributions to season's NTC (out of 100%):
1st: Wilma (12.9%)
2nd: Emily (12.2%)
3rd: Rita (10.0%)
4th: Dennis (9.0%)
5th: Katrina (8.7%)

Highest Intensity (pressure and wind):
1st: Wilma (882mb and 160kts)
2nd: Rita (895mb 155kts)
3rd: Katrina (902mb 150kts)
4th: Emily (929mb and 140kts)
5th: Dennis (930mb and 130kts)

1st: Katrina (1336)
2nd: Stan (80)
3rd: Dennis (42)
4th: Alpha (26)
5th: Wilma (22)

1st: Katrina ($75 bil)
2nd: Wilma ($12.2 bil)
3rd: Rita ($10.0 bil)
4th: Dennis ($2.2 bil)
5th: Cindy ($0.3 bil)

Also, CSU's April forecast for the 2006 season was just issued today and is available at: http://hurricane.atmos.colostate.edu/Forecasts/

Please visit my tropical Atlantic headquarters.