25 November 2013

2013 Atlantic hurricane season wrap-up: least active in 30 years

My 18th annual season summary is available on the Washington Post's Capital Weather Gang blog:

2013 Atlantic hurricane season wrap-up: least active in 30 years

Thanks for sharing another hurricane season with me, and for your continued interest.

18 November 2013

New disturbance in central Atlantic... Melissa?

It's been 25 days since the National Hurricane Center issued any advisory on an Atlantic tropical cyclone, but that streak could end shortly.  A large trough and upper-level Low pressure system has been gradually transitioning to a subtropical cyclone, and that in time could transition to a fully tropical cyclone.  The next name on the list is Melissa.

The subtropical nature is demonstrated by its origins as well as its current structure with fronts still attached to it.  The central pressure is down to 995mb, and tropical storm force winds already extend over 250 miles from the center.  It's nowhere near land... the closest reference point is Bermuda, roughly 750 miles west-northwest of this disturbance (centered near 29N 53W as of this post: see basin-scale map).

It is expected to drift slowly to the north over the next couple of days, then accelerate into the icy waters of the north Atlantic tropical cyclone graveyard.  The sea surface temperature under the storm is a comfortable 27C now, but in about 4 days, the SST will be around 20C and this system will certainly have transitioned back to an extratropical cyclone by then.

26 October 2013

Hurricane Mitch: 15 years later

With the combination of a dormant Atlantic right now and another significant anniversary today, I thought I'd write a short summary on Hurricane Mitch, one of the most intense, destructive, and deadly hurricanes in history.

On October 26, 1998, it achieved tropical cyclone perfection in the western Caribbean with a peak intensity of 180 mph (and 905mb central pressure).

Not only was it so close to Honduras and Nicaragua at this intensity (strongest winds were still offshore), but it virtually STALLED, taking five days to drift onto and across Honduras.  In the track map below, the large red circles represent Mitch at its most intense, then it weakened as it drifted slowly southward to landfall.

Although the peak winds may have died down prior to official landfall, the rain did not.  Up to 3 feet of rain fell in southern Honduras, but extreme totals were recorded over much of Central America.... and 10"+ amounts were also recorded in many parts of Mexico and then an isolated area in southern Florida as well.  Unofficial local reports in Honduras were up closer to 6 feet of rain.  Mudslides and flooding were especially devastating in Honduras, where about 70% of the country lost power, fresh water, transportation, and communication.

Mitch was responsible for approximately 19,000 deaths across ten countries, but the vast majority were in Honduras (14,600).  It remains the second deadliest hurricane in Atlantic history, trailing slightly behind the Great Hurricane of 1780 that claimed over 22,000 lives in the eastern Caribbean.

Here's your opportunity to stare a Category 5 hurricane in the eye!  Back in 1998, I made a high-resolution visible satellite loop available that is zoomed in over just the inner core.  I know there are folks who were subscribed to my email list/blog back then who are still subscribed, and I remember sharing the details of this monster hurricane with you as it unfolded, including this satellite loop.

This year, at the end of October, we don't have a Mitch, Wilma, or Sandy to worry about... the Atlantic is quiet for now.

24 October 2013

Hurricane history: Sandy and Wilma


One year ago this morning, Sandy intensified to a hurricane just south of Jamaica.  By the morning of October 25th, it rapidly intensified to a Category 3 hurricane with 115mph winds as it made landfall on the southeastern coast of Cuba.

Visible satellite image of Hurricane Sandy on the morning of October 24, 2012.
Model guidance was coming into better agreement on a track that would bring Sandy into the New Jersey coast as a very large cyclone on October 29th, possibly not tropical, but still very potent.  Below is a clip from my blog post one year ago:
"The ominous forecast by last night’s ECMWF deterministic run places an incredibly strong cyclone off the New Jersey coast on Monday evening... with tropical storm to hurricane force winds covering every state between Virginia and Maine. A scenario such as this would be devastating: a huge area with destructive winds, extensive inland flooding, possibly heavy snow on the west side, and severe coastal flooding and erosion."
To read the rest of that post, see Sandy strengthens to hurricane on approach to Jamaica; odds of East Coast impact grow


Another significant hurricane anniversary is that of Hurricane Wilma in 2005.  On the morning of October 19th, Wilma smashed rapid intensification AND intensity records in the Atlantic when a reconnaissance plane found a central pressure of 882mb.  It went on to hit the Cozumel/Cancun area of the Yucatan peninsula as a high-end Category 4 hurricane, then turned sharply to the northeast with a bullseye on the Florida peninsula.

Wilma's track... intensity is color-coded, and dates are marked at 0000 UTC (the "24" marker is  0000 UTC on Oct 24, or 8pm EDT on Oct 23).
Eight years ago today, Wilma plowed into the southern tip of Florida as a Category 3 hurricane.  I have several long radar loops of Wilma available at http://andrew.rsmas.miami.edu/bmcnoldy/tropics/radar/index.html#wilma05, and a satellite image from shortly after landfall is shown below.

Nearly all of south Florida (west and east coasts) was without power after Wilma went through, and wind gusts over in the Miami/Fort Lauderdale/West Palm Beach area were in the 100mph range.  It left a swath of destruction and flooding from the Keys up to north of Lake Okeechobee.

Not only is it the 8-year anniversary of Wilma's landfall on Florida, it's also the 8-year anniversary of the last time a major hurricane made landfall ANYWHERE in the U.S.!  For a more detailed description of just how odd this major hurricane landfall "drought" is in the U.S., see my blog post from nine days ago: Tropics extremely quiet in Atlantic; record drought in major U.S. hurricane landfalls

As always, thanks for reading and sharing!

23 October 2013

Lorenzo, and an update on the season

On Monday morning, Tropical Storm Lorenzo formed in the middle of the Atlantic (it was initially Tropical Depression 13).  The closest reference point would be Bermuda, but it was even 650 miles southeast of that.  Today, Lorenzo remains a weak tropical storm, and is in a hostile environment with 30kts of vertical shear.  A recent satellite image shows an exposed surface circulation with all of the thunderstorm activity displaced well to the southeast.

As of 5am today, the intensity estimate was 45kts, and it's forecast to weaken/dissipate over the next couple of days.  It will remain very far from any land.  To put its location in another perspective, it's 1900 miles due east of Daytona Beach, FL... the same distance as it is between New York City and Salt Lake City.

As an aside, one year ago today I was writing about newly-formed Tropical Storm Sandy when it was south of Jamaica.  For a haunting trip down memory lane, here's my blog post from October 23, 2012.  Sandy's U.S. landfall occurred on October 29, six days after that post was written.

In the big picture, the season remains extremely quiet... one of the quietest on record.  Although we've had twelve named storms, there have been just two short-lived Category 1 hurricanes, and no major hurricanes (Cat3+).  Going back to 1950, only four other seasons had zero major hurricanes: 1968, 1972, 1986, and 1994.  Of course, this season isn't over yet and we could still have one or more major hurricanes, but as of now, 2013 joins this short list.  In terms of ACE, the season is at about 30% of an average season for this date, and there is nothing expected to form in the foreseeable future.

09 October 2013

South Florida hurricane climatology... and major hurricane landfall drought

I wanted to take today to revisit a post that I made last year... and is still just as relevant. The first part focuses on hurricane landfall climatology in south Florida, one of the most vulnerable and frequently-hit areas in the country.  The second part briefly takes a look at the continued absence of major hurricane landfalls on the U.S.

As we head further into October, the fifth month of the official Atlantic hurricane season, it’s very important for folks in south Florida to realize that this is the greatest hurricane risk month. More hurricanes directly hit or affect southern Florida in October than in any other month. In the graphic shown below, the gray circle is 300 miles across and centered on far western Broward County – designed to include all of southern Florida and immediate surrounding ocean. Any storm of hurricane intensity (sustained winds of 75mph+) whose center passed within that circle is shown in the colored lines, and the legend in the lower right corner associates the color with a category on the Saffir-Simpson scale (yellow is Category 1, orange is Category 2, etc). Finally, the coastal counties are shaded by historic landfall frequency, with darker reds corresponding to more frequent, and pale reds corresponding to less frequent. The monthly tally of tracks passing through the circle is indicated in parentheses below the month. Keep in mind that all of these storms were hurricanes – tropical storms and depressions are not included; and most importantly, never focus on exactly where the center of the track is. Destructive winds, tornadoes, flooding rains, and inundating storm surges can and do occur for hundreds of miles away from the center; so even tracks on the fringe of the circle likely brought severe weather conditions to the mainland.

Another interesting aspect of these maps is that in August and September, southern Florida is most likely to get struck by a storm coming from the southeast. But in October, the dominant direction is from the southwest… due to storms coming from the Gulf of Mexico and western Caribbean, the more favored areas for hurricane formation later in the season.

On the topic of landfalls, do you remember the last time a major hurricane made landfall on the U.S.? It was Hurricane Wilma, on the morning of October 24, 2005, and it hit southwestern Florida at Category 3 intensity. That was 2,908 days ago, an utterly unprecedented span between major U.S. hurricane landfalls. 

Going back to 1900, this graph shows the number of days between consecutive major hurricane landfalls on the U.S.  This helps to put the current span in perspective.  (Adapted from http://rogerpielkejr.blogspot.com)
Streaks that even approach this long are very rare, and only two other spans of over 2,000 days have occurred since 1900. Why has it been so long? Pure luck. There have been several major hurricane landfalls since 2005 in other countries (Nicaragua, Mexico, Cuba, Virgin Islands, Bahamas, and close encounters in Jamaica and Belize), so it definitely isn’t correct to say that seasons since 2005 have been quiet … far from it. No one knows exactly when our lucky streak will end, but I can say with 100% certainty that it will end eventually!

If one does not occur during the remainder of the 2013 season, then looking ahead to August 1, 2014 (for example) would bring the span up to 3,204 days.

05 October 2013

Karen getting ripped apart before landfall

Wind shear and dry air have persistently whittled away at Tropical Storm Karen.  The surface circulation is now exposed almost entirely... the only deep convection to be found is 80+ miles to the southeast.  Karen will pose only a minimal threat to the northern Gulf coast when it comes ashore early Sunday morning.

Enhanced infrared satellite image of Karen from 7:45am EDT.  I marked the storm's center with a red X to help you find it.  (NOAA)

The wind shear (difference in wind speed and direction between low levels and upper levels of the atmosphere) is up near 30kts this morning, and may decrease to 20kts or so this evening, then ramp up to 50kts+ as it gets absorbed by a mid-latitude trough and cold front.  Generally, shear over 20kts is toxic to a tropical cyclone.

Dry air also continues to infiltrate the storm's circulation... even without shear, that can be enough to choke the life out of a tropical cyclone, after all, the fundamental mechanism that drives them is latent heat release (the energy released when water vapor condenses into cloud droplets and rain).  The image below is a model analysis from this morning showing mid-level winds and relative humidity.  Karen is centered just south of eastern Louisiana, and the dry air (brown shades) can be seen swirling into it.

500mb winds and relative humidity from the 06Z NAM analysis. (twisterdata.com)
At 8am EDT, Karen was located 155 miles south of Morgan City, LA and heading north at 10mph.  It is forecast to make a turn to the northeast later today.  Peak sustained winds are estimated to be 40mph, but that could be generous... it's actually difficult to find observations to support that.  All hurricane watches have been discontinued, but tropical storm warnings remain in effect for most of eastern LA, and a tropical storm watch extends eastward to Indian Pass, FL (see map).  This section of the Gulf coast really dodged a bullet this time... Karen could have been so much worse (think Camille, Opal, Katrina, etc).

The latest watches and warnings, as well as the track forecast, can be found on the National Hurricane Center's website.

Early morning model analysis of surface winds, with weather station wind observations plotted.  Definitely not a big wind maker for anyone!  (wunderground.com)

Storm Surge
The storm surge danger has greatly diminished - the latest models suggest a slight chance of a 2-4' surge in the New Orleans area eastward to Biloxi. 

As with any landfalling tropical cyclone, there is the possibility of tornadoes, and today's highest risk is extreme southeastern LA.

Inland Flooding
Since so much of Karen's moisture is already being dissipated, the rainfall expected from it in the coming days is also decreased.  The latest 5-day forecast from WPC shows most of the rain associated with Karen dwindling by the time its remnants reach Georgia.

I have long radar loops up and running which could be interesting, but as it looks now, it will just be disorganized heavy rain well to the east of the center.

03 October 2013

02 October 2013

Caribbean system may become Tropical Storm Karen and affect Gulf and East coasts

An update on the tropical disturbance in the western Caribbean is available on the Washington Post's Capital Weather Gang blog:

Caribbean system may become tropical storm Karen and affect Gulf and East coasts

Also, thanks to everyone who read, shared, and helped make Monday's blog post such a big hit.  Even amidst the major government shutdown news yesterday, that article was the 4th most popular item on the entire Washington Post website on Tuesday afternoon!

01 October 2013

Jerry falling apart, Karen in the works?

When Tropical Depression 11 formed on Saturday night, the outlook was never very bullish for it.  It was upgraded to Tropical Storm Jerry on Monday morning, but was heavily sheared and disorganized.  Today, it is still located in the central Atlantic (about 2200 miles east of Cape Canaveral FL, or 1500 miles west of the Canary Islands) and is losing a battle with very dry air and moderate shear.

Enhanced satellite image of TS Jerry from 7:15am EDT today.  Low clouds show up as yellow, and you can see the exposed low-level circulation center in the middle of the image. (NOAA)
At 5am EDT, the maximum sustained winds were estimated at 45mph, and it has basically stalled in place due to a lack of steering flow.  By the end of the week however, the shear may relax a bit and it should begin moving to the northeast, so IF it doesn't completely fizzle out (yes, that's technical) by then, it could hang around as a weak tropical storm through the weekend... still very far away from any land.

Strength (colors) and direction (white lines) of the current steering flow for Tropical Storm Jerry.  It is stuck in a col between ridges. (CIMSS)

Elsewhere, a persistent area of disturbed weather over the central Caribbean Sea has been festering for nearly a week.  Today, it has migrated a little further west and is centered near the Honduras/Nicaragua border.

Although it's disorganized now, the environmental conditions generally favor gradual development in the near term.  If it reaches tropical storm intensity, the next name on the list is Karen.  By the weekend, it is expected to move into the Gulf of Mexico and be greeted by very dry air and increasing vertical wind shear.  The latest batch of model guidance is in good agreement on a track toward the Yucatan peninsula, then into the central Gulf, then somewhere along the northern Gulf coast.  The timing varies greatly among the models, so there's still large uncertainty.  Though some of these track forecasts may be alarming, NONE of the guidance currently indicates that this will reach hurricane intensity, and by the time it reaches the U.S. coast, its largest impact will likely be heavy rain.

Track model guidance from the 06Z run today.  (U of Wisconsin-Milwaukee)
Stay tuned for any developments -- we need to watch this Caribbean disturbance very closely... the western Caribbean and southern Gulf are climatologically favored regions for hurricane formation in early October!

30 September 2013

What happened to hurricane season?

Tropical Storm Jerry has just formed in the central Atlantic, but like most storms this season, it would be easy to miss.  Today's post takes a look at the unexpectedly quiet hurricane season so far and can be found on the Capital Weather Gang blog:

What happened to hurricane season? And why we should keep forecasting it…

17 September 2013

Another Bay of Campeche storm in the making?

Since my last update on Sunday, Ingrid made landfall near La Pesca (Mexico) early Monday morning as expected, but weakened slightly and crossed the coastline as a tropical storm.  Of course, tropical storms are still capable of producing very heavy rain.  It continues to dissipate inland over mountainous areas of Mexico, but the flash flooding caused by both Ingrid (Mexico east coast) and Manuel (Mexico west coast) is responsible for at least 50 deaths now.

Humberto is back in the picture again... still in the central Atlantic and no threat to land.  It's located about 1000 miles WSW of the Azores and is a tropical storm with 45mph sustained winds.  Models and the NHC forecast it to become a sub-tropical cyclone shortly, then an extratropical cyclone or even open trough in a few days as it heads toward Iceland.

Visible satellite image of the Atlantic... with Tropical Storm Humberto on the far right, and the U.S. east coast on the far left.  For scale, Humberto is centered 2300 miles due east of Daytona Beach, FL.  (NOAA)
Now, on to the new disturbance, which once again is located near the Yucatan peninsula and headed for the Bay of Campeche.  If this sounds familiar, it should!  Back in May, Barbara snuck in from the eastern Pacific and then dissipated in the Bay of Campeche.  Other storms have since plagued the area, including Barry (June), Fernand (August), Tropical Depression 8 (September), and Ingrid (September).

Enhanced satellite image of the disturbance near Belize and the Yucatan peninsula. (NOAA)
In the near term, models agree on gradual development and a WNW track into the Bay of Campeche tomorrow.  Environmental conditions appear to be favorable (<10kts of shear, >29C SST, moist mid-levels, etc) for intensification in the foreseeable future, so this could easily become TD 11 then TS Jerry this week.

In the longer term (beyond 4-5 days), it's possible that this system will stall in the Gulf of Mexico and get picked up by a passing trough, which would allow for a track toward the northern Gulf coast.  This is a scenario that will be closely watched with each new set of model runs.  The alternative would be a track very similar to Ingrid's.

15 September 2013

Hurricane Ingrid to hit Mexico tonight

Ingrid did what so  many storms in the Bay of Campeche do: intensify really fast in a small amount of space.

In the past 24 hours (09Z yesterday - 09Z today), the central pressure fell just 5mb, but the winds increased by 25kts.  Further intensification is expected, perhaps reaching Category 2 status at landfall overnight.  One key factor in limiting really rapid intensification is actually another tropical cyclone!  Tropical Storm Manuel is on the other side of Mexico and the upper-level circulation over each cyclone is producing wind shear over the other.

Tropical Storm Manuel in the East Pacific, and Hurricane Ingrid in the Gulf of Mexico are "attacking" Mexico from both sides today.  (CIRA/RAMMB)
Ingrid is located about 150 miles east of Tampico, and tracking northwest at 7mph.  Maximum winds are 85mph and it is expected to make landfall .  Again, rainfall will be a major concern, with 1-2 feet forecast over a fairly large area.  Along the coast and to the north of where it makes landfall, a 3-5 foot storm surge is expected as well.  Extreme south Texas could also get several inches of rain from Ingrid in the coming days.

Unfortunately, radar coverage of landfall is hindered due to technical problems with the radar in Altamira, Mexico.  The radars in Alvarado, Mexico and Brownsville, Texas are too far away.  However, there are a variety of satellite loops available at http://andrew.rsmas.miami.edu/bmcnoldy/tropics/atlantic/

Elsewhere, Humberto has temporarily weakened below Depression status, but is being watched for likely regeneration... still in the middle of the Atlantic.

12 September 2013

TD10 forming in Bay of Campeche, Gabrielle and Humberto update

All signs point to Tropical Depression 10 forming in the Bay of Campeche this afternoon.  The disturbance that I mentioned in Tuesday's update has crossed the Yucatan peninsula and is now back over water.  As the models predicted, it is taking shape and getting better organized.

Afternoon visible satellite image over the southern Gulf of Mexico.  (CIRA/RAMMB)
As I write this, an aircraft is en route to reconnoiter the developing storm, but earlier today, a satellite that measures surface wind speeds passed over the area and observed what certainly looks like a closed circulation to me.

Surface winds as seen from the ASCAT instrument at 12:25pm EDT today showing a circulation centered in the middle of the Bay of Campeche.  (OSI SAF)
I also have radar loops available at http://andrew.rsmas.miami.edu/bmcnoldy/tropics/radar/ where you can monitor the progress of the storm when it's close to the coast.  The loop from Sabancuy started at 7am EDT today and shows it leaving the peninsula.  The loop from Alvarado will be handy in the coming days.

The model guidance remains in agreement on the track and intensity (in general).  While there are some differences, the system is expected to move quite slowly to the W or WNW toward Mexico, and intensify.  At the moment, the strongest it is forecast to get is a minimal hurricane, but most models keep it at tropical storm intensity with a landfall sometime early next week.

The next name on the list is Ingrid.


Gabrielle weakened to a Depression when it was at its closest approach to Bermuda, but has since re-intensified to a Tropical Storm.  It's now about 200 miles NW of Bermuda, but this last gasp will be short-lived.  Environmental conditions will soon become too hostile and it will dissipate as it heads toward an encounter with Nova Scotia on Friday evening.

Enhanced satellite image of Tropical Storm Gabrielle on Thursday afternoon.  The strong thunderstorms (white) are far displaced from the surface circulation (yellow).  Bermuda is southeast of the storm. (NOAA)

Humberto has now been a hurricane for nearly two days, and it might have one more day to go before it weakens.  It is located about 460 miles northwest of the northernmost of the Cape Verde islands.  The figure below shows the past track in gray, the current location as a red hurricane symbol, and various model forecast tracks in colored lines.

11 September 2013

Humberto becomes first hurricane of the season

Within hours of breaking the record for latest date of first hurricane formation, Humberto was upgraded to a hurricane at 5am EDT today based on its satellite presentation.  The record holder is still Gustav, which became a hurricane at 8am EDT on September 11, 2002.
 (Note that operationally, advisories come out at 5am, 11am, 5pm, 11pm EDT (09Z, 15Z, 21Z, 03Z), while in the "best track" database, values are recorded at 2am, 8am, 2pm, 8pm EDT (06Z, 12Z, 18Z, 00Z).

So, Gustav (2002) and Humberto (2013) will have to share Sep 11th, then Diana (1984) has Sep 10th, then Erin (2001) has Sep 9th.

This morning, Humberto remains a minimal hurricane and is located about 300 miles west of the Cape Verde islands.

The track forecast remains the same... head north for a couple days then make a sharp turn to the west when it encounters a strong subtropical ridge.  By that time, the wind shear is expected to be quite strong, so it's forecast to weaken back to a tropical storm.  The image below is zoomed out quite far to give you a perspective of where it is and where it's going.  The last "S" marker is the NHC forecast position on Monday.

The disturbance near the Yucatan peninsula has indeed continued to develop, and is now consolidating near the Mexico/Belize border.  The central pressure is down to 1009mb, and though it will likely lose some of its organization as it crosses the peninsula, it is expected to make a quick comeback once it hits the Bay of Campeche tomorrow morning.

Infrared satellite image of the disturbance heading into the Yucatan peninsula.  The bright colors indicate very cold, high cloud tops found over intense thunderstorms.  (CIRA/RAMMB)
Model track guidance is keeping the future storm further south, making the southern Texas option less likely.  As far as intensity goes, models top out at a strong tropical storm, so it's not a huge concern... just heavy rain for Mexico, but the same part of Mexico that already got hit by TS Barry, TS Fernand, and TD 8 this year.  More on this tomorrow once we see how it fares crossing land.  If it becomes a tropical storm, the next name is Ingrid.

As expected, Gabrielle is losing its punch as it heads into cooler waters and higher shear.  As of this morning, it's just a skeletal cyclone; all that remains of it is a low-level cloud swirl.  Maximum sustained winds are 50mph according to the 5am EDT advisory, and it is centered just a few miles west of Bermuda (the magenta mark in the image below).  It is still expected to reach Nova Scotia by Friday night, probably not as a tropical entity though.

Enhanced satellite image of Gabrielle passing by Bermuda on Wednesday morning.  Low clouds show up as yellow, while high clouds show up as white.  (NOAA)

09 September 2013

Humberto forms, could become season's first hurricane

This week is the climatological peak of the Atlantic hurricane season, but this year, it arrives with little fanfare.  Though there has not been a single hurricane yet, that could change very soon.

On Sunday evening, Tropical Depression 9 formed just off the African coast from a potent easterly wave.   This morning, it was upgraded to Tropical Storm Humberto, the ninth named storm of the season.  It is presently centered just south of the Cape Verde islands and tracking west at 12mph.

Enhanced infrared satellite image of Humberto at 8:30am EDT this morning.  (CIRA/RAMMB)
It is forecast to become a hurricane by Wednesday.  If you recall, the latest date of first hurricane formation in the aircraft reconnaissance and satellite era (back to 1944) is September 11, and that record was set back in 2002.  Specifically, it was 1200 UTC on September 11, and when it comes to the record, hours might count.  The 5am EDT forecast from NHC today brings Humberto to hurricane intensity at 0600 UTC (2am EDT) on the 11th.  But based on current appearance and trends, I'd suspect that the timeframe will be nudged forward/sooner.

Since 1851, 34 storms formed or passed within 100 miles of where Humberto did (18 of which were in September).  As you can see below, the tracks of these storms have large variability, ranging from a quick recurvature to long-tracked major hurricanes that plow into the U.S.  The current official forecast track for Humberto would be the quickest and furthest east recurvature off all of these.

Past tracks of all known storms that formed or passed within 100mi of where Humberto formed.
Models are in fairly good agreement on the quick recurvature scenario too, so the odds of it becoming a threat to land are extremely small.

Select model forecasts as well as the NHC forecast for Humberto, from the 0600 UTC runs today. (NCAR)
The name Humberto has been in the rotation since 1995 (that is, it has been used in 1995, 2001, 2007, and 2013).  It replaced Hugo, which was retired in 1989 after its devastating landfall on South Carolina on September 22 of that year.  In all likelihood, it will stick around for another reincarnation in 2019!

Elsewhere, the remnants of Gabrielle are still hanging around between Bermuda and Hispaniola.  The environment is likely going to remain too hostile for any tropical redevelopment, but it could become a stronger subtropical or extratropical cyclone and potentially impact, Bermuda, Newfoundland, or Nova Scotia.

07 September 2013

Gabrielle, TD8, and eastern Atlantic disturbance

Since my last update on Thursday, Tropical Storm Gabrielle dissipated due to a combination of shear, dry air, and land interaction with Puerto Rico.  However, the remnants are still very much trackable, and are showing signs of regeneration now that the system is north of Puerto Rico and Hispaniola.

Enhanced satellite image of former Gabrielle.  The center (marked with a red L) is nearly exposed on the northwest side of the deep convection.  The sharp boundary of the high clouds there is indicative of strong vertical shear.  (NOAA)
Though over very warm water (29C), the vertical wind shear is up near 30kts and is not expected to relax in the foreseeable future.  That will be the primary factor in inhibiting its regeneration.  NHC is giving it a 40% chance of formation over the next 5 days, and I would agree with that number... IF it reforms, it would be working against the odds.

The track guidance is all over the place, largely due to the uncertainty in whether or not it regains some sort of organization.  Not all models agree on that, so of course, not all models agree on a similar track. 

Moving on to TD8... if you sneezed, you missed it.  It formed yesterday afternoon in the extreme southwestern Gulf of Mexico, right on the coastline, and then dissipated inland early this morning.  It was never named -- just a short-lived Tropical Depression.

Elsewhere, there is a strong easterly wave located approximately 700 miles west of the Cape Verde islands.  It exited the African coast back on Sept 2.  As you can see below, it's not very well organized at all yet.

Most models bring it N-NW for another day or so, then flatten out to a more W course for several days.  Even in five days, it will still be short of the Lesser Antilles, so there is time to see how this one evolves.  I'll add additional details in a future post, but for now, it's at least worth pointing out.

01 September 2013

Disturbance heading into eastern Caribbean

An easterly wave that left the African coast about a week ago is just about to cross the Lesser Antilles and enter the eastern Caribbean.  It has been inactive for most of the journey, but has gained organization and persistent deep convection over the past 24 hours.

Enhanced satellite image over the Lesser Antilles on Sunday afternoon.  (NOAA)
The environmental conditions are presently conducive for further development, and are expected to remain so for at least the coming week.  It is in 5-10 kts of vertical shear, over 29C sea surface temperatures, and the mid-level humidity is high enough to support growth.  You can view a radar loop of it as it passes through the islands here (new frames continuously added, so check back later too).

Forecasts of intensity, track, shear, SST, and mid-level humidity from a small selection of models.
So, we will clearly have to watch this closely, as model solutions range from near-nothing to a Category 3 hurricane in 5 days near Jamaica.  Right now, it's too soon to get concerned, but not too soon to pay attention.  HWRF, the model solution in blue on the plot above, is interesting because it has the storm becoming a minimal hurricane by mid-week, then weakening slightly as it crosses Haiti and eastern Cuba, then picking back up with a possible track toward south Florida next weekend.

5-day forecast from an HWRF run today... valid Friday afternoon.  The colored contours are surface wind and the black line contours are surface pressure.

28 August 2013

Remembering Katrina

Today, August 28th, is a day many in the hurricane community will never forget.  It was a Sunday morning, and we started the day off staring in disbelief at what had become an enormous Category 5 hurricane sitting in the central Gulf of Mexico - and heading north.

Katrina as a Category 5 hurricane on August 28th, 2005.  (NOAA) 
It hit Miami, FL three days prior as an intensifying Category 1 hurricane, and strengthened as it crossed over the eastern Gulf. The forecast was, and had been, accurately centered on eastern Louisiana and Mississippi for several days; the big question leading up to that landfall would be the intensity.

For many years, the "New Orleans scenario" was well-known, and had been addressed in practice drills and exercises... it's a very vulnerable city, with many areas situated below sea level.  Everyone knew this would be bad; really bad.  The NWS forecast office in New Orleans issued the following warning in advance of the landfall:


Of course, as dire as that sounds, the end result was even worse.  It made landfall on the morning of August 29th... it would become the costliest natural disaster in the history of the U.S. (~$108 billion), and was responsible for nearly 2,000 deaths.  The only good news was that it weakened quite a bit prior to landfall, and came ashore as a weakening Category 3 storm (120mph winds) rather than the Category 5 (175mph winds) it was a day earlier.  Watch a radar loop of the landfall... and note that the final frame also marks the time the radar there was destroyed.

It generated a devastating 27.8-foot storm surge in Mississippi, and the smaller surge in New Orleans was enough to stress the levees protecting the city beyond their breaking point.  Many beachfront communities were erased from the map, particularly in Mississippi.

Observed storm surge generated by Katrina.  The peak value in the ">16 feet" category was nearly 28 feet in Pass Christian, MS... the largest surge ever recorded in the U.S.  (SURGEDAT)
Later that year, other major hurricanes (Cat3+) made U.S. landfall, wrapping up with Wilma on October 24th when it hit the southwestern Florida peninsula.  That remains the last time the U.S. was hit by a major hurricane.  I included some details on just how bizarre and unprecedented this span is in my season wrap-up last year (scroll down to the 7th paragraph).

25 August 2013

Last week of August comes with increasing activity

As I eluded to in Friday's update, the tropical Atlantic is primed to start cranking out some storms, especially toward the beginning of September.  But even now, a couple areas of interest are brewing: one rapidly organizing system in the southern Gulf of Mexico and another near the African coast.

First, the disturbance in the far southern Gulf of Mexico.  This is an African easterly wave that was located back over the Lesser Antilles on the 19th, and got more convectively active on the 22nd.  Since then it passed over the Yucatan peninsula and just emerged into the Bay of Campeche recently.  It has been surprisingly quick to get organized, and an aircraft reconnaissance plane has been tasked to investigate it later this afternoon.  The aircraft could possibly find it to be a tropical storm... if so, the next name on the list is Fernand.  Fernand is a new name this year, replacing Felix from 2007's list.

Disturbance in the Bay of Campeche, heading west toward Mexico. (NASA)
Even if it does continue to intensify, its time before landfall is very limited.  It's heading generally westward, which brings it over land by this evening.  It is already showing up nicely on radar... I have a long radar loop from Alvarado available (Invest 95L).  As usual for weaker systems, the largest threat will be heavy rain and flash flooding.

Shifting our attention 5200 miles to the east, a wave has just exited the African coast and though it doesn't look too impressive just yet, several global models do forecast it to get organized over the next several days as it heads W-WNW across the deep tropics.  It's coming off at a more typical latitude, centered near 10N 18W, and the environment appears to be favorable for development.  I will provide additional details on it as the week goes on. 

Visible satellite image of an easterly wave coming off the African coast.  (CIMSS)

23 August 2013

Update on activity (or lack thereof) so far this season

With all of the forecasts for an active Atlantic hurricane season, it seems a bit odd that there have been no hurricanes yet, and we're heading into the last week of August.  For an update on the conditions and expectations, check out my post on the Washington Post's Capital Weather Gang blog:

Where the heck are all the hurricanes??

16 August 2013

Both Atlantic systems weaken

In the past 24 hours, both Erin and the disturbance near the Yucatan have lost a lot of steam.

The Yucatan system is just now about to enter the Gulf of Mexico, but the surface circulation is devoid of deep convection, and a strong upper-level low to its north is introducing hostile vertical wind shear.  In the images below, the left one is an enhanced infrared image which allows you to see the low clouds in yellow and the higher clouds in white... and the right one is a water vapor image, which mostly shows what's going on in the upper atmosphere.  I added basic low-level features in green and upper-level features in red for clarity.

Since it is now reduced to just a low-level circulation, it should track more toward the west-northwest, rather than turning toward the north.  This shifts the longer-range landfall location to Texas or northern Mexico... but, "landfall" makes it sound more significant than it really is.  Wherever it goes, its biggest impact will be heavy rain -- perhaps not even that!

However, if it does head more westward, environmental conditions would improve for the disturbance in a couple days, perhaps allowing it to regain a little organization.  The current "worst case" model (which still isn't TOO bad) is HWRF, which strengthens it into a hurricane and shows a landfall near Brownsville on Monday night.  Other models are less bullish.

Surface wind (shaded contours) and surface pressure (line contours) according to the most recent HWRF model run.  Not a likely solution, but one with a slim possibility, and worth being casually aware of at least.
The key to the evolution of this system will be if it goes more west than north, and if new deep convection can develop and persist near the center.  If not, then it can be written off.

Much further east, Tropical Depression Erin is gradually heading into drier air and cooler waters as expected.  It is also now reduced to a skeletal cloud swirl centered about 400 miles west of the Cape Verde islands.  It would need to hang around for another three days or so until it tracks into a slightly more favorable environment... but still not ideal.  Most models dissipate the storm within the next 3-5 days, and track it northward into the north-central Atlantic graveyard.

Tropical Storm Erin west of the Cape Verde islands.  (NRLMRY)

For a bit of hurricane history, on this date in 1992, the season's fourth tropical depression formed 700 miles west of the Cape Verde islands.  On August 17th, it was upgraded to the season's first tropical storm: Andrew.  Seven days after getting named and significant intensification, the tiny Category 5 hurricane plowed head-on into Florida, just south of Miami.  It is one of just three Category 5 hurricane landfalls on the U.S., and the most recent.  Do you know the other two??