09 November 2009

Ida still heading for US coast...

Since my last update when Ida had just crossed into Nicaragua, it continued north into the western Caribbean, then between Yucatan and Cuba as it intensified to a Category 2 hurricane.  It's now a CAT1 storm, but heading straight north toward the MS/AL/FL Panhandle area.  Landfall there is expected very early tomorrow morning as a strong TS or minimal hurricane.

The hurricane doesn't look too impressive on satellite... the convection is mostly offset to the north of the circulation due to 30kts+ of vertical wind shear.  The SST is 27C and decreasing with time.

You can see the latest Tropical Storm and Hurricane Watches/Warnings at http://www.nhc.noaa.gov/storm_graphics/AT11/refresh/AL1109W_NL+gif/
Please visit my tropical Atlantic headquarters.

05 November 2009

Ida forms in southwest Caribbean...

On Wednesday afternoon, TD11 formed just off the northern coast of Panama.  It doesn't appear to have come from an easterly wave, but rather a persistent area of convection that sat and festered for a week or so.  At such a low latitude, it takes quite a while for the Coriolis effect to influence the circulation of a low pressure.  Later on Wednesday, an aircraft found that it had sustained winds high enough to warrant upgrading it to Tropical Storm Ida.  On Thursday morning, it was again upgraded to Hurricane Ida (3rd hurricane of the season), with sustained winds of 65kts and a central pressure of 987mb.  It's presently located right on the east-central Nicaraguan coast and looks well-organized for being so close to land.

The forecast is for gradual weakening as it spends a day or so over Nicaragua and Honduras, then for gradual strengthening as it heads NNW into the Gulf of Mexico and toward the central US gulf coast.  Any US landfall is still a week or more away.

Please visit my tropical Atlantic headquarters.

06 October 2009

Grace comes and goes, Henri forms in central Atlantic...

For completeness, I'll briefly mention that Tropical Storm Grace formed on Oct 5 near the Azores Islands.  It reached a peak intensity of 60kts and then lost tropical characteristics as it headed toward Ireland.  It is currently spreading heavy rain over Wales.

At 21Z today, Tropical Storm Henri formed 600 miles east of the Leeward Islands.  Its origins are an African easterly wave that exited the continent back on September 30.  The intensity is estimated at 35kts and 1007mb, and is expected to weaken in the face of increasing wind shear.  It is no threat to any landmass or island.

Please visit my tropical Atlantic headquarters.

18 September 2009

Fred possibly making a comeback, new disturbance in central Atlantic...

Fred was initially classified as a Depression back on Sep 7, then was a major hurricane on Sep 9, dissipated on Sep 12, and after traveling 2000 miles westward as a low-level swirl, is finally making a convective comeback.  However, it won't be an easy path to regeneration... the vertical wind shear is quite strong from the north and expected to only relax slightly in the 1-2 day timeframe.  The SSTs under the storm will be ample to support a strong storm (28-29C) if the shear ends up being less than forecast.  A number of computer models intensify Fred over the next several days as it tracks fairly slowly to the WNW-NW.  The remnant circulation is located about 500 miles of Puerto Rico.

The other feature of interest is a slow-moving easterly wave that exited the African coast on Sep 10 and is now located near 13N 40W, or about 1400 miles east of the Windward Islands.  Similar to the remnants of Fred, the vertical shear is prohibitive for significant strengthening in the foreseeable future.  Some models do show it intensifying in the 4-5 day timeframe.  The next name on the list is Grace should it get named.

Please visit my tropical Atlantic headquarters.

08 September 2009

Fred forms in far eastern Atlantic...

On Monday afternoon, the easterly wave I referenced on Friday (was inland over western Africa then) was upgraded to Tropical Depression 7, and was further upgraded to Tropical Storm Fred just 6 hours later.  Since then, Fred has continued to get better organized and the latest intensity is 60kts and 990mb.  It is located about 350 miles southwest of the Cape Verde islands and tracking west at 12kts.

The satellite presentation is very impressive... there is healthy symmetric outflow, persistent cold cloud tops over the center, and microwave imagery reveals an eye and eyewall.  Fred is forecast to become the second hurricane of the season in the near future, and start heading NW into the open central Atlantic.  In the longer term, the same trough that will be responsible for steering Fred NW will also introduce a much less favorable environment and the storm should weaken notably by the end of the weekend.

Please visit my tropical Atlantic headquarters.

04 September 2009

Erika dissipates, new easterly wave developing...

Earlier today, NHC wrote their final advisory on Erika, which was downgraded to a Tropical Depression on Thursday.  In the face of strong mid-level wind shear, the low-level circulation was completely removed from the mid- and upper- level circulation and convection.  The remnant circulation is now south of Puerto Rico and will we monitored for any signs of redevelopment.

Elsewhere, a potent easterly wave is located just south of the Cape Verde islands and tracking W at 18kts.  There is a 1012mb Low associated with the wave.  On satellite imagery, it has an impressive presentation, both in the low-level circulation and attendant convection.
However, most computer models do not develop THIS wave, but rather the one behind it, currently over western Africa.

Please visit my tropical Atlantic headquarters.

01 September 2009

Erika finally forms in central Atlantic...

Since leaving the African coast one week ago, this easterly wave has remained intact, but struggled with shear.  Today, an aircraft reconnaissance flight revealed a closed circulation with 45kt sustained winds at the surface and a 1007mb central pressure.  So, it was immediately upgraded to TS Erika.  It's heading WNW at 8kts, and is located about 400 miles east of the Leeward Islands.  A Tropical Storm Watch has been issued for the northern Leeward Islands.

The official forecast is for gradual strengthening, but not quite reaching hurricane intensity, and to continue heading WNW.  By Friday, it should be just north of Puerto Rico... and in the longer term, this is a storm that the US east coast should be keeping an eye on.  A majority of forecast models bring Erika up to CAT1-2 intensity by the weekend.

Please visit my tropical Atlantic headquarters.

31 August 2009

Disturbance closing in on Leeward Islands...

The easterly wave I mentioned on Friday has still not been upgraded to a Depression or Storm, but certainly looks like a weak Tropical Storm on satellite imagery.  It is now located about 600 miles east of the southern Leeward Islands and heading WNW at 12kts.  Nearly every computer model forecasts it to intensify to a hurricane by mid-late week.  SSTs in its path are 28-29C, and vertical wind shear is minimal (and expected to remain so for several days).  The next name on the list is Erika.

Danny weakened as it approached the coast Friday night into Saturday and NHC ceased writing advisories on it before it was even near the US or Canada.

Please visit my tropical Atlantic headquarters.

28 August 2009

Danny expected to recurve short of US coast...

The disturbance that I mentioned in my previous update on Tuesday has since been upgraded to TS Danny and has tracked northwest toward the southeast US coastline.  As of this morning, Danny was located about 350 miles south of Cape Hatteras NC and heading NW at 9kts.  The storm has consistently been poorly organized, with an exposed low-level center and the convective activity displaced to the east of the center.  Latest intensity is 35kts and 1008mb, and that is not expected to change much as it makes its way toward the coast then gets pushed out northeastward, scraping the US/Canada coast.

Danny is forecast to be near Cape Hatteras overnight tonight, then near Cape Cod on Saturday evening, over Nova Scotia on Sunday morning, and Newfoundland early Monday morning.  However, the effects will likely be minimal since it's not a strong storm and it'll be moving rather quickly.

Elsewhere, another easterly wave exited the African coast on Monday and has gradually gotten better organized.  It's located about 650 miles WSW of the Cape Verde islands and has a 1010mb Low embedded in it.  It is strongly favored by computer models to become the next hurricane by the end of the weekend as it heads WNW toward the Lesser Antilles.

And finally, an easterly wave is just now exiting Africa today and also shows signs of development.  The next two names on the list are Erika and Fred.

Please visit my tropical Atlantic headquarters.

25 August 2009

New disturbance being watched north of Leeward Islands...

An easterly wave that exited Africa on Aug 18 (the same one that I mentioned was near 35W last Friday) has very slowly gotten better organized and is now centered near 22N 64W... or about 400 miles north of the Virgin Islands.  It is being invigorated by an interaction with an upper-level Low to its west.

This wave is expected to continue to develop over the coming days and follow a path not too different from Bill.  That is, head WNW toward the US coast, then recurve offshore and turn to the NE, passing by Nova Scotia and Newfoundland.  However, this system may get closer to the US coast than Bill did, and even has the potential to clip the extremities such as NC, MA, and ME this weekend.

Since my previous update on Friday, Bill exited the scene after brushing by Nova Scotia and hitting eastern Newfoundland.

Please visit my tropical Atlantic headquarters.

21 August 2009

Bill heads NW between Bermuda and US...

Not much has changed since my last update on Wednesday.  The storm has weakened a bit to 95kts and 957mb, and has begun its more northerly track to the west of Bermuda and to the east of the US coast... it's currently about 700 miles southeast of the North Carolina coast.  Although it won't make a direct landfall on Bermuda or the US, it will (and has been) produce very large waves on Bermuda and all along the entire eastern seaboard of the US and Canada.

Here are measurements being recorded by a buoy in Bill's path (wind/pressure and significant wave height):

And from Bermuda (surface observations and radar loop):
http://www.weather.bm/observations.asp (if it asks for username/password: guest/guest)

In the longer term, Bill is expected to scrape by Nova Scotia on Sunday, then Newfoundland early Monday as a potent storm... transitioning from tropical to extratropical.

Elsewhere, a couple of easterly waves are producing healthy convection in the far eastern Atlantic... one near 30W and one near 18W.  The majority of forecast models do not develop either of these, but that could change with time.

Please visit my tropical Atlantic headquarters.

19 August 2009

Bill strengthens to a Category 4 hurricane...

Since yesterday's update, Bill went from 90kts to 115kts and from a central pressure of 963mb to 950mb.  Those figures are as of 15Z today.  As I type this update, a reconnaissance aircraft is heading into the core of the storm to determine the latest winds and pressure.  Hurricane Bill is located about 1000 miles SSE of Bermuda and heading WNW at 16kts.  This motion is expected to turn more NW then N in the coming days, avoiding the US coast, but perhaps threatening Bermuda, Nova Scotia, Newfoundland.  Environmental conditions are favorable for additional strengthening, and Bill is forecast to reach 125kts before encountering higher shear and cooler water in 5-6 days.

If the aircraft presently investigating the storm finds anything significantly different than the current intensity, I'll likely send out another brief update, otherwise, it'll be tomorrow.

Please visit my tropical Atlantic headquarters.

18 August 2009

Bill a Category 2 hurricane...

Three days ago, Bill was a Depression.  Now it's a 90kt hurricane on a strengthening trend.  An reconnaissance aircraft left St. Croix this morning to investigate the storm, and will be arriving in the eyewall within a couple hours of this writing.  At that point, the intensity could be adjusted (the transition from satellite-only intensity estimates to in-situ aircraft measurements can sometimes result in a false intensity change if you're looking just at the numbers).

At 15Z today, Bill was located at 15.9N 51.2W and tracking WNW at 14kts.  Intensity was 90kts and 963mb.  The track will follow a WNW trajectory for the next few days, gradually becoming more NW then N as it heads into a weakness in the subtropical ridge in 4-5 days.  While this scenario spares the US coast, it puts Bermuda in the target zone this weekend.  The storm is expected to intensify further, reaching CAT3 or 4 status in the next couple of days.

Please visit my tropical Atlantic headquarters.

17 August 2009

Ana, Bill, and Claudette made for a full weekend...

What was TD2 made a slight comeback over the weekend, and was upgraded to Ana.  However, it still struggles to get better organized, and has since been downgraded to TD Ana.  Presently located between Puerto Rico and Hispaniola, it is being further shredded by the mountainous terrain on those islands.  The forecast track brings it over Hispaniola and into south Florida in three days, but only as a Depression.  The primary threat associated with it will be flooding.

The potent easterly wave I had been mentioning all of last week was finally upgraded to TD3 on Saturday morning, then TS Bill on Saturday afternoon, then Hurricane Bill on Monday morning.  It continues to strengthen as it heads WNW at 14kts.  The latest intensity is 80kts and 977mb.  One significant change from the end of last week is the projected track of Bill.  It has moved northward quite a bit, which should result in it recurving prior to reaching the US coast.  However, it could potentially mean big trouble for Bermuda by this weekend.  Bill should be in the vicinity of Bermuda as a very strong hurricane by then.

And finally, Claudette formed just off the Gulf coast on Sunday morning.  I believe it originated from the same easterly wave I referenced way back on August 1 when it exited the African coast.  On the 4th it was near 35W, on the 10th it was near 60W, and on the 16th it was near 85W.  Fortunately, it did not intensify very much before heading inland over the western FL panhandle on Monday morning as a 45kt Tropical Storm.

Please visit my tropical Atlantic headquarters.

14 August 2009

TD2 dissipates, easterly wave getting organized...

TD2 succumbed to the shear and dry air and is now just a tiny low-level cloud swirl with intermittent bursts of convection.  It will be watched for regeneration though, but is not much of a concern in the near future.

On first glance, the easterly wave behind TD2's remnants looks very similar, but it is a much larger circulation, has its primary inflow from the south rather than the north, and the moderate vertical shear will be letting up within the next 12-18 hours.  Given these conditions, it is forecast to gradually intensify as it heads W-WNW.  At its current speed, it would be near the Lesser Antilles on Wednesday, quite possibly as a hurricane.
Although it's presently only 600 miles west of Africa, long-range models (8-10day) are already painting an ominous picture for the US coast by late next weekend.  It's too far out to say exactly where, but the timing at least serves as a heads-up for coastal residents.

Recall from my update three days ago that the last time the first named storm formed this late in the season was Aug 17, 1992: Andrew.

Please visit my tropical Atlantic headquarters.

13 August 2009

TD2 barely holding on...

Since yesterday, TD2 has seemingly ingested quite a bit of that stable dry air I mentioned, and is now nothing more than a low-level swirl of clouds.  The small circulation is also especially prone to even moderate vertical wind shear, which it's experiencing.  These conditions combine to give a small likelihood that TD2 will reach TS intensity in the foreseeable future.
As of 15Z today, the intensity was estimated at 25kts and 1008mb and it was located about 1400 miles east of the Leeward Islands.

On the other hand, the easterly wave on its heels still looks like something to keep a close eye on.  It's presently about 250 miles SSE of the Cape Verde islands and tracking W at 12kts.  It's still disorganized, but has a very definite circulation, persistent convection scattered around the center, low vertical shear, 28C SSTs, and is embedded in a large pocket of deep-layer moisture.
This disturbance is expected to gradually develop and head WNW toward the Caribbean over the next 5 days.

Please visit my tropical Atlantic headquarters.

12 August 2009

TD2 slowly organizing...

A combination of low-level stable air and moderate easterly wind shear is keeping TD2 below Tropical Storm intensity.  The latest intensity estimate is 30kts and 1006mb, and still heading W at 11kts.  The forecast track has changed very little since yesterday.  TD2 is still expected to reach TS status later today.

Elsewhere, the potent easterly wave I referenced yesterday has now exited the African coast and will be monitored for development.  Several computer models suggest this could become a storm to cause concern in the distant future.

I wanted to point out that my webpage at http://einstein.atmos.colostate.edu/~mcnoldy/tropics/atlantic/ is a little different... I reorganized the links.  So you might need to hunt around a bit at first to find your favorite resources, but hopefully the new system will work out better for people.

Please visit my tropical Atlantic headquarters.

11 August 2009

Second Tropical Depression of the season forms in far eastern Atlantic...

Two and a half months after TD1 formed off the northeast US coast, TD2 forms near the Cape Verde Islands off the west coast of Africa.  This is peculiar in two ways: it's rather late in the season to have the second Depression form, and it's rather early to have the "Cape Verde season" kick in.  The easterly wave that became TD2 was over Chad on August 4, and exited the African coast on August 8, so it has been a feature of interest for some time.  There's actually another potent easterly wave now located over Guinea, but that'll be a topic for a future discussion.

At 15Z today, TD2's intensity was estimated at 25kts and 1006mb.  It is located at 14.6N 29.6W and tracking W at 11kts.  It is embedded in an area of dry air (negative factor), it is over 27C water (neutral factor), and is in an area of minimal vertical shear (positive factor).  By this weekend, it may begin to feel a weakness in the subtropical ridge begin to move a bit more NW, potentially avoiding the Lesser Antilles.

It is forecast to become Tropical Storm Ana within a day, but maintain weak TS status for the near future.
The last time the second Depression formed this late in the season was 2000 (August 13, became TS Beryl).  The last time the first named storm formed this late in the season was 1992 (August 17, became Hurricane Andrew).

Please visit my tropical Atlantic headquarters.

04 August 2009

Easterly wave making its way across Atlantic...

On August 1, a potent African easterly wave exited the coast and is now centered near 35W.  There is evidence of a mid-level circulation in the satellite imagery, and a hint of a weak surface circulation based on microwave scatterometer and visible satellite data.  It has also maintain a small cold cloud shield over the center of the mid-level circulation.  This system, though poorly organized now, could become better organized in the coming days.  It would reach the Lesser Antilles this weekend if it holds together.

Elsewhere, the basin is quiet.  However, this is not atypical... climatologically, there is only one tropical storm by this date, and no hurricanes.  The first name on this year's list is Ana.

Please visit my tropical Atlantic headquarters.

20 July 2009

Disturbance heading into eastern Caribbean...

An African easterly wave, generated over the Ethiopian Highlands back on July 6 exited the African coast on July 13, and is now located just east of the Lesser Antilles.  It has very slowly gotten better organized, and has a mid-level circulation and persistent deep convection near the center.

The disturbance is expected to continue tracking W-WNW at 15kts through the northern Caribbean over the next several days.  If it does manage to organize, it would become TD2 then TS Ana.  However, it's moving into the northern periphery of a Colombian High where vertical shear is excessive.  In the near future, islands in the Lesser Antilles can expect some rather stormy conditions for a couple days.

Please visit my tropical Atlantic headquarters.

08 July 2009

Bertha now on a weakening trend...

After peaking out at 105kts earlier today, Bertha has since encountered stronger vertical shear and drier air, and is now deteriorating.  At 21Z today, the intensity was estimated at 75kts and 980mb, tracking NW at 10kts.  The CAT1 hurricane is located at 22.7N 54.8W.  The deep convection is shifted  almost entirely to the northeast of the low-level center, a true sign of the stronger vertical wind shear.

Bertha is the 6th strongest pre-August hurricane on record, and the 5th earliest pre-August hurricane.  The combination of these traits yields the 3rd strongest hurricane so early in the season (105kts on Jul 8).  Only Audrey (6/27/57) and Alma (6/8/66) were earlier AND stronger.  Bertha also shattered the record for furthest east formation for a pre-August tropical storm, hurricane, and major hurricane.  Thanks to Phil Klotzbach and Jeff Masters for pointing these climatological features out!

It is possible that in a few days, conditions will improve slightly and the storm will be allowed to once again intensify.  Bermuda should still be watching this, but it seems more and more likely that Bertha will recurve just east of Bermuda given the current 4-5-day forecasts of the weakness in the subtropical ridge.

Elsewhere, a large easterly wave is just exiting the African coast today, but has little circulation associated with it, and none of the forecast models indicate development.

Please visit my tropical Atlantic headquarters.

28 May 2009

Tropical Depression 1 forms before the official start of hurricane season...

Much like last season, this season is getting a slight jump start.  In 2008, Arthur formed on May 31, and now, TD1 has formed off the US east coast.  It came as no big surprise however, as it has been festering since early in the Memorial Day weekend in the Bahamas. 

In the past 24 hours, it has gotten much better organized.  Yesterday at this time, it was a vigorous low-level swirl off of Cape Hatteras.  Today, is has persistent deep convection over the center, and is taking advantage of low vertical shear and the relatively warm waters in the thin ribbon of the Gulf Stream.  It has about a day to intensify further before an approaching trough will increase the shear and nudge it over cold sea surface temperatures (SSTs).  At 15Z today, the TD1 was located at 37.3N 71.0W and heading NE at 15kts.  Maximum winds are 30kts with a minimum sea level pressure of 1007mb.  It is forecast to track NE toward the open north Atlantic... a menace only to shipping.  If it reaches 35kt+ intensity, it would be upgraded to TS Ana.

To everyone who has joined this mailing list since last season ended, welcome!  I try to keep the updates and discussion brief yet informative; hopefully insightful when necessary.  If you ever have a question about a term or phrase I use, please just ask.  This list includes people from all walks of life... from grade school teachers, military personnel, hurricane researchers, business owners, resort staff, professors, students of all ages, friends, family, media, etc.  Although I may occasionally express surprise at a discussion or forecast made by the National Hurricane Center, it is my policy (and my university's policy) to report their official positions and forecasts, so please do not ask me for my own personal forecast... especially regarding landfall.

Please visit my tropical Atlantic headquarters.