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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So you think TD3's beautiful outflow and banding is unimpressive?
It looks terrible. Not sure if a downgrade may be coming.
Yep. We definitely don't need a storm in South Florida. I watched Storm Stories on the Weather Channel with Hurricane Andrew and it was incredible the destruction. People were saying their last words to each as they fit their whole family in a single bathroom. Makes you wonder how people can wish for these things to come to their doorstep.
eh I dont think you should be worried, they are very far away
GFDL has Ana moving more West and evetually taking it into the Gulf while it takes TD3 which is further South (11.5N) well north to become a fish storm!!
How is the weakneed in the ridge affecting less on Ana then on TD3!?
Rapid intensification?
Large ugly banding. I can see it's low level circulation through the thin high clouds.
I agree, both systems looks crap in IR - Bill looks okay in visible though...both lacking any convection to speak of..
Really not believing the rapid intensification on nay of these two systems.. NO way!
Maybe stormno was right about it developing. He was wrong on it being Ana, although it looks better then Ana.
most sensible post of the day...
I completely agree. Been through a couple of Hurricanes now and don't want to see another. I was north of Fort Lauderdale when Andrew hit; but got to see the damage upfront and personal the day after. One storm knocked out power for 15 days. Nope, don't want anything coming in this direction. And don't wish this on anyone.
MY Melodramatics? Please. Don't flatter yourself.
How fast?
WS couldn't hold back anymore. Talk about going off the deep end.
how does a storm have low longitude? lol.
how can you say no troughs in site? the models are coming into agreement on there being a trough coming down to sweep TD3/Bill out to sea.
Your right 90L is now TD#3 WU has not removed it from the page sorry your post was lost :)
OMG go watch Tiger play already
Drak has mentioned nothing but actual facts,both systems are having issues with the dry air pockets in the tropical atlantic.Maybe this new 12z GFDL run is a sign of things to come with TD3 and like i previously said the ECMWF might not be wrong with a recurve of this system out to sea.
That is what I was thinking convection is decreasing and it doesn't look so good but I guess its circulation was enough to get the classification
as for Ana I think it could end up downgraded to a TD soon xD
I went down to help clean up after Andrew. It looked like someone dropped an atomic bomb on Naranja, Cutler Bay and Homestead. I told myself then that I would never see anything like that again in my life.
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