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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Pat wins.. I have no idea
I think Adrian was making fun of the posters on here.. he knows well that this is well out and the models almost always change.
you can have your mode runs lol
the mode runs are trash at this time way too soon to tell what bill will do
ECMWF develops it
Buoys are quite capable of measuring 84 mph winds in 56 foot waves. I know most of the moored ones have a 50-foot tether.
And I want to fess up. I have been holding out on you. I am a met. My job is to build hurricane wind fields based on all available observations for the sake of storm surge modeling. I, and my office, have done this for about 8 years and have done so for USACE, NASA, NOAA, coastal engineers, forensic studies.
We use a fair bit of analysis when there are no surface obs and I agree that the radar is showing some nice mid-level turning...but that does not always mean surface low. Maybe it is and maybe it is not there right now, but will be soon. Still a possibility it doesn't do much, if any, development.
Hey, anyone know what model was supposed to get assimilation of the WSR-88D data? Was that starting this year?
Bertha effected Bremuda. Bertha wasn't a fish.
Yeah...like in Georgia, the angle of the coast makes it rare for a hurricane to hit there.
Can I wait till we get a Red Light..?,I Like da red Lite Challenge the best...
I would say its moving NW look at this long loop...
They believe that 120 hours the trough will be in place to curve Bill out to sea. But they had it earlier as the ridge holding in place and Bill pretty much slams Florida. So they will flip flop back and forth the next couple of days before we really find out whats going to happen. All depends on the trough, it could stall out or Bill might relocate its COC.
sunday mode runs may have it runing in too FL
As long as it is short lived it's nice. We did have to skip the HUGE 200 year family reunion today though due to the rain and mud.
Let us all know when you have a shift in your winds there!
It loses based on Humberto alone. I am sure there are more, too.
thanks for the warning. actually even stormW puts up pictures like this in a fun manner. so he would also be at risk? i assume... not?
We're all in FL, and the Gulf States are wishing the same here. Time for a NE hit. Let the gulf coasts rest a bit!!
Many, many storms have done that. Major hurricanes, in fact, have done that. Not uncommon at all.
i wouldn't go that far on a dean/emily hit. High is not near that strong however it is a very big possibility that bill could outrun trough and get closer to conus before recurving. I believe models are recurving it way to quickly. If I remember yesterday afternoon all models except for one had it going towards florida
looks like itll have time to develop watch out folks
If you know of them, who were you before then? Can't work both ways you know.
1999 Hurricane Bret
2007 Hurricane Humberto:
2001 TS Allison:
Stormjunkie is outta town this weekend...he'll be around again Tuesday...
Let's not get carried away...Um, I mean, thanks.
*aggie doesn't handle compliments well*
i am in contact with jp and he says that it is too early to tell anything about the long range track for bill
They could add to certain situations...like Humberto (I suppose we will never forget that name)
The coverage is limited, you are correct.
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