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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Especially if it continues on that WNW track that is forecast. A slight shift south in the track would have it traversing almost the entire length of Hispanola and Cuba. That would certainly mean death for a weak storm with such a small circulation, just as you said. Then again, any small deviation north or south of that would have it over water for the majority of the time. It's something to watch.
A, B, C, or D?
I think the models expect ana to be a weaker system not gaining much strength from now until it reaches the islands.. which is why they but it on a West track
Me? I wasn't talking to you.
LMAO, BTW stormwatcher I have a bad feeling about these 2 storms , I just don't see them going that far north especially at that forward speed.
Very interesting...Thanks!
Yes it can, 99% won't.
Huh? Like what? Tropical?
A lot can and likely will happen between now and when Ana gets near or into the Caribbean. If it continues sheared like it is then it will have less time to intensify and the Eastern Caribbean is not the most hospitable place for a weak system.
I am still not convinced that it is out of the woods from all the dry air and shear but time will tell on that score.
Here is a buoy that Ana is approaching and is now about 120 miles east of. Pressure there down to 1008 now.buoy
long term models are inaccurate
Well Taken, I could say the same thing regarding your comment, it wasn't meant for you also. Even now! Enough said, lighten up and enjoy the weather chat and be safe this season.
If you notice, the models (some time back) were calling for Ana to have gained latitude, enough so to have crossed 15 degrees by now. If you look you can see the center moving almost due west. The models will probably trend further south if the system continues this movement. Cayman is not out of the woods either because of this.
As we have a fair, and growing, number of visitors, and others that do not spend nearly as much time looking at the data as many of us, I am going to point out a few sources of links to models, satellite data, surface obs, etc.
http://www.stormjunkie.com/pages/trophome/trophome.php Thanks to our own StormJunkie
http://www.adriansweather.com/tropicalweatherlinks.htm Thanks to our own hurricane23
http://www.wunderground.com/tropical/ WU tropical page has more links to good data than you might think!
http://www.wunderground.com/blog/atmoaggie/show.html Not that it really belongs with the rest of these, but they are my personal favs and in my blog they will stay.
If you found your way here, you can find your way to the WU tropical page or my blog. And you should be able to follow those links to most any data you might be seeking.
This has been a public service message. Feel free to remind anyone at anytime where they can get links to anything tropical.
Checkmate
Gustav and Ike were major hurricanes. Ana is just a weak tropical storm. Anyways, if Ana were to strengthen it would most likely take a northern path bringing it to Florida. So, I'm gonna go out on a limb and say the GOM is safe from Ana (which is a good thing).
/Users/jpenabel/Downloads/2009AL03_4KMIRIMG_200908152045.GIF.gif
thanks !!
Following the GFDN it might could appear similar to hurricane Dean.
Another day closer to the 20th anniversary of Hurricane Hugo,
I just wanted to thank all of y'all for your great tropical explanations and insights. Keep it up!
Now...if someone could just wish-cast me a tropical system into Central Texas, I'd much appreciate it (massive, massive drought here).
Yeah, that's why I think SFLA is not even close to being out of the woods. If Ana gains strength, it would take the northern part of the NHC's cone.
Just last blog We proclaimed Cayman the Hurricane Capital of the World.
Time of Latest Image: 20090815 2045 UTC
2km Storm Relative IR Imagery with BD Enhancement Curve
The same infrared imagery shown in the earth relative framework is displayed in a storm relative framework, with a 2km resolution and enhanced with the "BD Curve" which is useful for directly inferring intensity via the Dvorak Enhanced IR (EIR) technique. Scaling is provided by two lightly hatched circles around the center. The two circles have radii of 1 and 2 degrees latitude, respectively
Oh ok, I wasn't sure if you were referring to me or the troll.
Either you are being funny, kind of, or my real goal was not met.
WOW you must be so impressed by it your Caps Lock key got stuck.
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