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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You need to check the AB high in about four days once we have a core system that is feeling the mid to upper levels of the atmosphere and then check the steering flow in said levels.
I agree, nothing is getting out.
Yep, you're keeping the halo shiny!
Just a estimate right now going simply by history.
I am a changed person.. nothing but S&I now :)
http://www.canetalk.com/2009/08/1250392862_1250392732.shtml
TS Bill
TS Ana
I no which looks better and stronger
I looked at the loop that winter123 posted. Looks like 91L may be heading WNW for now. My question is probability of development. So far, shear in the GOM is low. 91L does have some circulation to it. SSTs are in the right range for development. Guess we just have to sit and wait. Remember, the big "K" developed in this area. 8-O
Seriously, being prepared was a tremendous relief at a very anxiety provoking time.
Great minds think alike.
That was just my exact thought.
Looking forward to the rain it will bring us here in Florida tomorrow.
Upper right hand of the comments section - adjust your filter.
It means a number of people have seen the posts, and clicked on the - sign in the upper right of the comment block
Past 48 hours, it really is not possible for us to know what's going to happen. All we can do is to watch and see. As for the models again, I will not start to believe them until I see consistency over a few consecutive runs, with the system actually following the track plotted in the model forecast. So with the models currently expecting them to be moving to the WNW and to have them actually going to the W or WSW, doesn't that show you they may not have a great handle on the current situation?
So yes as I said, let's be patient and wait and see. There's no need to panic, and overreact. If you live anywhere from lets say...Hispaniola and the Gulf Coast all the way to the Canadian Maritimes just watch the progress. Because Ana or Bill could easily affect anywhere in between there.
just food for thought
Nice !!
Ana continues to hang on. I have never thought that it would amount to much with all the dry air and shear.
Hahaha, Press!!
Have a look at this loop. Look what goes up the west coast of Florida, then watch the train continuing to roll off Africa.
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