Ana and TD 3 take aim at the Lesser Antilles
Tropical Storm Ana was born this morning, when the remnants of Tropical Depression Two made a comeback and organized into the first tropical storm of the 2009 Atlantic hurricane season. Ana is the latest first named storm of the season since Hurricane Andrew got its name on August 17, 1992. The two storms have some similarities, as Andrew formed in the same part of the ocean, and also struggled in its early days with high wind shear and dry air. Let's hope the similarities end there.
Ana is struggling this afternoon. After an modest burst of heavy thunderstorm activity prompted NHC to upgrade Ana to a tropical storm early this morning, Ana has run into strong upper-level winds from the west that are creating high wind shear. This shear was not forecast, and it is not clear how long it will last. The shear has acted to drive dry air into the core of Ana, destroying almost all of Ana's heavy thunderstorms. The low-level center of the storm is now exposed to view, something that often foreshadows the death of a storm. It is possible the shear will destroy Ana, and several models (the GFS and ECMWF) forecast this may be the case. However, the shear forecast calls for shear to drop into the low range, 5 - 10 knots, tonight through Tuesday. If the shear does drop as forecast, Ana should be able to moisten the atmosphere around it sufficiently to protest itself from the dry Saharan air that surrounds it (Figure 1). SSTs are 27°C today, and will increase to 28°C by Sunday. By the time Ana moves into the Bahamas, total ocean heat content rises steeply (Figure 2), and rapid intensification of Ana is possible, if the shear and dry air haven't disrupted the storm. The intensity forecast models, for the most part, predict a steady intensification of Ana to the threshold of hurricane strength five days from now. The HWRF model is on the strong side, predicting a Category 2 hurricane. The GFDL predicts a weak tropical storm five days from now, but that is because the model has Ana passing over the rugged terrain of Hispaniola, something the other models do not predict. In summary, the intensity forecast for Ana has higher than usual uncertainty, and I give equal chances that the storm will be a hurricane--or non-existent--four days from now.
Figure 1. Water vapor image from this morning showing the large area of dry, Saharan air surrounding Ana, and lying to the north of Tropical Depression Three. Image credit: NOAA/SSD
Tropical Depression Three forms, could be Bill later today
QuikSCAT data from this morning and satellite loops revealed that the tropical wave (90L) in the middle Atlantic has finally developed a well developed surface circulation and can be classified as Tropical Depression Three. Recent satellite imagery suggests that TD 3 may already be Tropical Storm Bill. Water vapor imagery (Figure 1) shows that TD 3's center consolidated a few hundred miles south of the dry air of the Saharan Air Layer (SAL). Thus, the storm should not be affected by dry air and dust as much as Ana has been. Ana may also act to moisten the atmosphere in front of TD 3, helping protect the storm from the SAL as it edges farther north over the the three days.
Figure 2. Heat content of the ocean, in kJ per square cm. Oceanic heat content steadily increases for Ana and TD 3 as they approach the Lesser Antilles Islands. Oceanic heat content levels of 90 kJ per square cm are frequently associated with rapid intensification of hurricanes. Image credit: University of Miami.
Wind shear is moderate, 15 knots, but is forecast to fall to 10 - 15 knots on days 2 - 5. Sea Surface Temperatures are about 27.5°C, and will remain in the 27.5 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow TD 3 to intensify steadily, and I expect the storm will be at hurricane strength by Wednesday, when it will be near the northern Lesser Antilles Islands. Most of our reliable intensity models strengthen TD 3 into a hurricane by Wednesday. Oceanic heat content (Figure 2) increases sharply just before the islands, so TD 3 could be intensifying rapidly as it moves through or just north of the Lesser Antilles on Thursday. TD 3 consolidated farther south than expected, so the track models calling for a more northerly path were probably incorrect. In particular, the ECMWF model, which had TD 3 turning sharply northwestward and missing the Lesser Antilles Islands, was probably much too far to the north in this morning's 00Z run. TD 3 will probably pass very close to the northern Lesser Antilles islands on Wednesday and Thursday.
I'll have an update Sunday.
Jeff Masters
Reader Comments
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What you don't wanna do, is say she's a TD on the verge of death, then she blows up again prior to hitting the islands and catching people unaware.
1)going through the 30 knt shear in the caribean
2)crossing cuba or hispanolia
You can never tell what Mother Nature has in store for us
Shep, my friend, gonna be a busy day here on the panhandle! Boats to secure, and preparations to make! I do believe that TS will be knocking on my door. Expect landfall between PCB and Destin tonight...
The NHC better hope that it doesn't spin up ala Humberto.
People will be screamin' "Why can't they predict a hurricane one day out!!!"
enough with the polls already... they are getting a bit old and are a waste of space. my comment on ur poll is also a waste of space
Actually, if Bill doesn't turn north, he will affect the islands in 4-5 days.
On the last Metsat loop it looks like it is starting to turn ot the NW. That is a sign that maybe the models are correct.
Thank you for your honesty. Quite an admirable trait. I am not an expert either, which is why I ask so many questions rather than contribute. One would not like to appear a fool amongst so many who DO know.
Yes, but Anna is sort of moisturizing that area to the West for Bill, so it won't go through the exact same conditions.
agree
If you look at the radar, it's doing just that, developing an eyewall.. Come on, lol.. water teps are 90 degrees and it's under an anticyclone, what do you expect?
2
and that surprised you? The Journal probably went to publication before midnight.... I will check the NWFL Daily later, it won't mention the storm either, I am sure!
Looks like the panhandle will have an interesting evening... hopefully since the TD is already so close to land it will not have time to get stronger. I expect to see winds around 50 sustained tonight. YUK
WOW, just what we want to hear !!!!!!!!!!!!
Tropical Update
LINK
I had a look... no Claudette yet
I haven't got it.
Please comment, this is a new blog, I hope you like it
really was a question aussie ....Geez
Good evening stormwatcherCI and to everyone else I bid you a Good Evening.
This is a worst case scenario in the making, though it will likely be much less than that.
A TC gets cooking on a Saturday, then blows up on a Sunday...then makes landfall before the work week begins.
Talk about a possible nightmare scenario...in my opinion...that's the worst possible.
Imagine if you decided to go camping on Friday...and you didn't listen to the radio.
Or...worst...you decided to go deep sea fishing, thinking everything was hunky-dory in the Gulf for the weekend.
Not good...
Good thing this is a "Dead" season that was written off by so many ppl here...
I am here too.... yep gonna be a wet one for us
I see that we now have three players in Atlantic.
Even though TD4 will most likely hit well to our east, it will bring up some of that nice tropical moisture and since it is already unstable out the wahzoo here, you cant rule out a full day of convection. I am not expecting a massive sotrm surge or strong winds but I do expect a day or two of rain.
I thought it was too. Watched it spinning on satellite and then radar from the very early morning hours yesterday. Then when the buoys had west winds, how could it not be a low? The pressures were not very low but relatively lower than the surrounding area. I guess that's all it takes. I'm no expert but have learned most of what I know from this blog when it comes to these starting.
I have followed the weather with great interest since childhood.
It was a pleasure watching it generate right on radar with this blog. Let's just hope it doesn't do much harm, and brings needed rain to someone who needs it. After all the rain it brought here, I know I won't have to water the tomatoes for at least today.
I'm 1500 miles out of position. And PensacolaDoug is celebrating his son's 15th birthday today...so he's out of position, too!
The entire XtremeHurricanes.com team is out of position for Claudette.
Not good....
Oz, good points! I have friends who left Friday to go to Port St. Joe to do some scalloping.... they are camping. Wonder if they have seen the forecast???
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