Atlantic Tropical Weather – 7/22/2010: Tropical Storm Bonnie & Tropical Depression #3

[Updated post]:

Tropical Storm Bonnie has formed in the Atlantic basin this afternoon.  Surface winds are now a sustained 40mph and the system is organizing itself more and more every hour.

T.S. Bonnie’s center is located near 22.7N, 75.4W; has maximum sustained winds fo 40mph; is moving NW @ 13mph and has a central pressure of 1006mb.

Bonnie has deep convection near the west side of her center.  Outflow is looking better in most quadrants.  She is still battling a strong upper-level low to her west, which has kept high vertical wind shear and dry air near Bonnie.  The storm’s center moved around during the day, resulting in some adjustment to the specific location of her probably future track.  The direction of her track will likely remain toward the NW/WNW, but is somewhat further north than it was earlier today.  As a result, Bonnie could pass closer to mainland Florida tomorrow afternoon before entering the Gulf of Mexico.  The official track still calls for a likely landfall near LA later this weekend (Sunday or later).

[Original post]:

Atlantic Basin Tropical Depression #3 has formed between the Bahamas and Cuba today.  The tropical wave that eventually developed a closed surface circulation has been moving across the Atlantic basin this week.  Heavy bursts of intense convection occurred the past three days as the wave passed along the northern Caribbean islands.

Given local weather features, T.D. 3 should intensify into a Tropical Storm later today but not intensify into a hurricane before making landfall somewhere along the U.S. Gulf coast (next week?).

T.D. 3′s center is located near 21.9N, 75.0W; has maximum sustained winds of 35mph (just below T.S. strength); is moving WNW @ 14mph and has a central pressure of 1008mb.

T.D. 3 will move through the Florida Strait (between FL & Cuba), likely right over the Florida Keys, entering the Gulf of Mexico tomorrow.  Thereafter, forecast models project a track envelope extending from southwest of Houston to south of New Orleans (~3 days from now).  The official track forecast from the National Hurricane Center shows the storm making landfall closer to the Lake Charles area.  While T.D. 3 (then T.S. Bonnie) won’t be a monster storm like Katrina or Rita, the projected tracks take the storm very close to the site of the Gulf Oil Disaster.  Work near the disaster site has been halted while officials confer on what the course of action should be as the storm evolves.

An Air Force Reserve hurricane hunter is on its way to the storm to gather additional data.  We will know later today whether T.D. 3 has intensified to T.D. Bonnie or not.

Atlantic Tropical Weather Update 8/16/09 #1

The drama in the Atlantic basin continues this weekend.  In the past few days, Tropical Depression Two reformed, then strengthened to Tropical Storm Ana.  Two days behind T.S. Ana, a vigorous tropical wave developed into Tropical Depression Three, then strengthened to Tropical Storm Bill.  Then, a tropical wave that had made its way near Florida interacted with an upper-level trough, sustaining deep convection over a couple of days’ time, developed into Tropical Depression Four overnight last night off the west coast of Florida.  The whole thing happened basically in five days time, but most of the action has taken place in ~24 hours!  So instead of appending updates throughout the day as I did yesterday, I’m going to put up separate posts.  This is Update #1 for 8/16/2009.

This morning, I’ll start with Tropical Depression Four since it is closest to U.S. interests.  Here are T.D. Four’s vitals:

Center located at 28.7N, 84.6W (76 miles SSE of Apalachicola, FL; 125 miles SE of Panama City, FL); moving NNW @ 14mph; maximum sustained winds of 35mph; minimum central pressure of 1011mb – that’s pretty high.

T.D. Four’s official track forecast has shifted considerably since I mentioned it last night.  It isn’t going to move across a good portion of the warm Gulf of Mexico, it’s going to move across a short portion of relatively cooler, shallower waters.  As such, it won’t have a lot of time to get organized before making landfall.  It is currently projected to make landfall just west of Panama City, FL tonight by 6PM.

About the only question is will it have enough time to organize/strengthen into a Tropical Storm before landfall.  The official intensity forecast is predicting that that will happen – about 2PM EDT today (~3 hours from now).  For a relatively new storm, it actually has some impressive organization to it.  I think it will be Tropical Storm Claudette by landfall tonight.  Amazing.  Post-landfall, the system will likely decay quickly Monday and Tuesday.  The threats to Florida and Alabama will be flooding and tornadoes.

Onto Tropical Storm Ana.  Here are T.S. Ana’s vitals:

Center located at 14.6N, 54.7W; moving W @ 20mph; maximum sustained winds of 40mph; minimum central pressure of 1005mb.

She’s picked up quite a bit of forward motion in the last day; the central pressure is still pretty high – no indication of rapid intensification in the next few hours.  Her location puts her 436 miles to the east of Martinique, in the middle of the Antilles.

T.S. Ana’s official track forecast has shifted significantly since last night, as I thought it might.  She is expected to shift her movement to the NNW today, pass over the Windward Islands in between Martinique and Guadeloupe, then move into the northeastern Caribbean Sea.  She is forecasted to continue over the south side of Hispanola Tuesday, then over southern Cuba Wednesday and Thursday before emerging over the Gulf of Mexico Thursday night.  In contrast, this time yesterday, the official track forecast put Ana over southern Florida by Thursday.  As such, the track forecast could certainly shift even further in the extended time period.  Most of the model solutions keep Ana on a more southerly route.  Only a couple show her moving to the north of the Caribbean islands in the 5-day forecast period.

T.S. Ana’s official intensity forecast keeps her as a Tropical Storm until moving over Hispanola, after which she should degrade to a Tropical Depression again.  Only one model intensity forecast strengthens Ana in the next few days to a strong Tropical Storm.  She’s simply battling too much dry air and wind shear to strengthen – she’s having a hard enough time maintaining herself.

Now, Tropical Storm Bill.  Here are T.S. Bill’s vitals:

Center located at 11.4N, 37.2W; moving W @ 13mph; maximum sustained winds of 45mph [update]: sustained winds @ 60mph; minimum central pressure of 1002mb.

T.S. Bill is undergoing a process of increasing organization and strengthening.  His official track forecast continues to keep him to the northeast of the Lesser Antilles in the extended forecast (4-5 days out).  I will note that that track forecast is on the southern portion of the model solution set – every model solution moves the storm more to the north in that 4- and 5-day forecast.

Bill’s intensity forecast is the interesting one for weather/hurricane fans.  Bill is forecasted to become a Hurricane by tomorrow and a Major Hurricane by Wednesday morning.  The good news is that intensification will happen far out to sea.  Combined with the favorable track forecast, Bill shouldn’t affect any landmasses with those strong winds.

Bill looks very organized this morning – a very good looking storm on satellite.  There is evidence of strong outflow in all quadrants around the storm – indicative of very healthy airflow.  I definitely think he will strengthen into a hurricane by late tonight – the sun has passed by his position already today, so he has today’s maximum ocean heat content to work with.  He is over 28C waters and will remain over that warm or warmer for a number of days from now.

Tropical Weather Update 8/15/09

[UPDATE 10:30P MDT]

Geez, after two and a half months of no activity in the Atlantic, the past week and especially the past couple of days has really seen the basin’s behavior shift dramatically.  I had previously ignored an area of disturbed weather off the west coast of Florida.  It was a tropical wave that made its way across the west Atlantic, interacted with an upper-level low for a couple of days and made its way across the Florida peninsula.  As of tonight, it has been designated an area of interest to the NHC: Invest-91.

It is relatively small in extent and has only limited organization and no central surface circulation yet, so the NHC is only giving it a <30% chance of tropical formation in the next 48 hours.  Surface pressures are falling in the general area of the disturbance.  Still, it is an area of interest as it is expected to move northwest across the Gulf and move ashore, according to recent projections, near New Orleans, LA.  I want to be clear: it is not expected to be a Tropical Depression, Storm or Hurricane at that time due to the latest information.  It is an area of thunderstorms that is expected to move ashore in a couple days’ time.  To fill out the picture, this disturbance is currently northeast of a Gulf Loop eddy in the Gulf of Mexico northeast of the Yucutan Peninsula.  The heat content of the Gulf under the expected path of this disturbance isn’t as high as in the eddy, but it is at least as high as the water near T.S. Bill.

Elsewhere, T.S.s Ana and Bill continue to move across the mid-Atlantic.  No significant changes in their track or intensity forecasts have been made.

A tropical wave has moved over the Atlantic from the west coast of Africa.  It looked fairly vigorous just prior to moving offshore.  It is relatively close to Tropical Storm Bill.  It isn’t expected to develop; I just wanted to make note of it.  The next wave over Africa is a few days away from moving offshore.

[UPDATE 5:30P MDT]

This has been quite the day for the Atlantic basin.  This morning, Tropical Storm Ana was announced.  This afternoon, Tropical Storm Bill was announced.  They are a couple of days’ distance apart in the middle of the Atlantic tonight.  I was thinking Tropical Depression Three was likely a Tropical Storm this morning, but the NHC prudently waited for additional evidence to declare it as such.

Tropical Storm Ana’s vitals are:  Center located at 14.4N, 50.4W; moving W @ 17mph; maximum sustained winds of 40mph; minimum central pressure of 1004mb.

Nothing to get terribly excited about, Ana is a healthy storm that is likely to get stronger as the days go by.  Ana’s official track keeps getting pushed to the south, resulting in major differences in the 120-hr forecast location.  As of tonight, the models place her anywhere from Southern Florida to south of Cuba – a significant difference to be sure.  Her movement over the next 12-48 hours will have a major impact on where she eventually moves.  Her official track forecast puts her over Hispanola Tuesday afternoon, across northern Cuba Wednesday and into the Gulf of Mexico Thursday afternoon.  That official track forecast is to the northern edge of the model solution envelope.  Moving over Hispanola and in close proximity to Cuba would likely keep the storm much weaker than if she were to remain over open waters, of course.  Every model solution does put Ana in the Gulf of Mexico in the extended forecast (>5 days).  With a great deal of heat content available, that would allow whatever was left of Ana to likely restrengthen and threaten Gulf Coast communities.  Stay tuned.

Tropical Storm Bill’s vitals are:  Center located at 11.3N, 35.2W; moving WSW @ 16mph; maximum sustained winds of 40mph; minimum central pressure of 1004mb.

Bill didn’t move to the southwest quite as much as the official center designation suggests.  Rather, the dominant central low skipped around a bit over the past day.  This low pressure center is well established, giving the operational folks and the modelers a much better idea of his current state and anticipated future behavior.

T.S. Bill is forecasted to keep moving around the subtropical ridge to his north, which would mean a more westerly, then northwesterly course in a couple of days’ time.  There will be plenty of ocean heat content ahead of him on the official track forecast and minimal shear, so Bill is forecasted to be a Category 2 storm in 5 days’ time.

T.S. Bill’s official track forecast still keeps him to the northeast/north of the northern Windward Islands 5 days from now.  Any alteration in the ridge’s strength and position will of course alter that track.  All of the models’ track forecasts indicate this behavior except for the UKMET, which keeps Bill further south and moves him over the Windward Islands by Day 4.  If the remainder of the models are more correct, it is liklier that Bill will remain out to sea, curving around the west periphery of the ridge away from the U.S. coast.

[UPDATE 10:30A MDT]

As I did last season, I will place updated information at the top of posts.  My earlier write-up can be found below.

New model guidance is out for Tropical Storm Ana.  In the official 3-5 day period, she is now forecasted to skirt the northern coast of Hispanola before continuing to the northwest and potentially affecting southeastern Florida.  That’s right: there is the possibility that T.S. Ana could make landfall over Florida Thursday.

The GFS and UKMET are two models that contribute to this official forecast.  They keep Ana to the north of the Caribbean Islands.  The GFDL models diverge from this solution and keep Ana to the south of Hispanola, over Jamaica and to the south of Cuba.  The GFS and UKMET have perfomed well so far in this very young season.

And Tropical Depression Three has officially formed.  It was interesting when I wrote the initial post a few hours ago that the NHC hadn’t upgraded the system yet -  probably because they needed additional satellite confirmation of wind speed and organization.  They got it.  T.D. Three’s vitals are as follows:

11.5N, 34.0W; moving WSW @ 17mph; maximum sustained winds of 35mph; central pressure ~1006mb.

T.D. Three is forecasted to move in a similar path that T.D.2/T.S. Ana has taken: generally westerly for the next day or so, then a gradual turn toward the northwest thereafter as a mid-/upper-level trough passes by to their north.  Thursday could find T.D. Three north of the Windward Islands.  It has a lot of ocean to cover before potentially affecting any land.  Between now and then, T.D. Three also has to contend with any cold water that T.S. Ana upwells as she makes her way across the basin.  Lots of action to come, I think.

—–

Well, the 2009 Atlantic Hurricane season has taken an interesting turn.  Last week, a tropical wave exited Africa near the Cape Verdes Islands.  It developed in Tropical Depression Two, but was held back from further development by dry, stable Saharan air to its north and west; high wind shear and relatively low water temperatures.  It decayed to a remnant low 36 hours ago and looked to slide into history.  Then, come convection popped up near the low’s center and the storm slowly matured yesterday.  It was forecasted to develop back into a Tropical Depression today if conditions held favorable.  Well, they’ve held favorable.  The system redeveloped into a Tropical Depression, then strengthened further into the Atlantic’s first named storm of 2009: Tropical Storm Ana.  Here are her vitals:

Center located near 14.6N, 46.8W; moving W @ 16mph; maximum sustained winds of 40mph; minimum central pressure 1005mb.

Ana is an extremely small storm, a result of the lack of development as she fought off the dry air, wind shear and low water temperatures.  Her environment should result in additional size development over the next couple of days, though she isn’t likely to grow to be a very large storm at her peak.

Ana’s official track forecast takes her over the northern-most Windward Islands Monday morning, and passing north of Puerto Rico by Tuesday morning.  I think it is likely she will be a Hurricane by Monday/Tuesday, but the official forecast keeps her at Tropical Storm strength through that period for now.

Invest-90 remains off to Ana’s east and the NHC has kept a >50% chance of tropical formation through the next 48 hours.  Like Ana, Invest-90 is going to pass over waters that are warmer in the next couple of days.  Combined with relativey weak wind shear, development of this system is highly likely.

Atlantic Tropical Weather Update 8/14/09

Tropical Depression Two fell apart so much yesterday that it was downgraded to a remnant low.  That means it didn’t have enough sustained convection to be considered a tropical system any longer.  Interestingly, the remnant low has developed convection around a central low again.  It hasn’t be re-upgraded, but the NHC is giving it a 30-50% chance of being upgraded in the next 48 hours.  It’s quite the interesting storm.  It is expected to keep moving west across the Atlantic over the next two days before turning northwest around the subtropical ridge to its north thereafter.  It should move over 28C waters in the next couple of days.  If it does, it has a higher chance of sustaining convection – nothing has moved over these warm waters all season.  Today’s official track forecast keeps the system to the northeast of the Caribbean Islands.

Further to the east is Invest-90, the broad area of low pressure with numerous convective storms slowly rotating around the center.  It’s organization (i.e. beginning of banded features & outflow aloft) has picked up since yesterday, as expected.  This disturbance should become the first named storm of the 2009 Atlantic season.  Here are its vitals as of this morning:

Center near 12.1N, 26.5W; moving W @ 14mph; maximum sustained winds of 30mph.

That westward motion should continue for the next 24 hours before making a slight turn toward the northwest through the 5-day period.  If this pans out, that would put the system near the northern Windward Islands by the middle of next week.  One of the models that performed well with T.D. 2′s motion, the GFS, is in the middle of the pack – it puts the center of this system just to the south of the most northerly Windward Islands.  GFS ensemble members generate a large fan-like set of solutions around the northern Caribbean and the southeast U.S. in its extended forecast.  Anywhere from Belize to North Carolina are in that solution set.  This isn’t too surprising given the large amount of time between now and the end of the forecast runs.  The official GFS track forecast is at the northern edge of that solution set through the first five days.

Every model is forecasting an increase in intensity over the next five days.  I expected the storm to reach Tropical Depression status already.  Such a designation is likely in the next 48 hours as the NHC gives the disturbance a >50% chance of doing so.  They note that organization has slowed down over the past several hours, but expect things to come together soon.

Lastly, a tropical wave is affecting areas near Cuba and Florida.  It isn’t expected to develop into a Tropical Depression.

[Update 5:30P MDT]:

The remnant low from Tropical Depression Two has regained enough convection, according to a NOAA high altitude jet, and almost enough organization to be reclassified as a Tropical Depression either later tonight or early Saturday.  It is currently centered 1000 miles east of the Lesser Antilles (Windward Islands) in the middle of the Atlantic Ocean.  The NHC has assigned it a >50% chance of tropical formation potential.

The broad area of disturbed weather that came off the African coast a couple of days ago also still has a >50% chance of tropical formation in the next 48 hours.  It has robust convection near the “center”.  Its organization has improved somewhat since earlier today, but will need to organize even further before attaining Tropical Depression status.  Right now, it is more elongated on an east/west axis than being circular.