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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I believe youre missing my point. Forgive me if youre not. I am aware that there are cyclones which develop quickly enough so that they are never officially classified as a TD. And i understand that although the 6-hour updates never consider these systems to be TDs, they were TDs at one point. Those cyclones are not the ones I am talking about. In most cases a TD is a required aspect of cyclogenesis, but not all. In some instances, a weather system may have 40mph+ sustained winds, and not be a cyclone. If these winds do not diminish, and the LLC closes off, then the system is instantly a TS, and at no point in its development could ever have been considered to be a TD.
You can say that again Drak.....
I was just checking in to see before I went to bed and all I could say was "What the Heck is this....
Taco :0)
Not sure I trust the SHIPs on that. Given how fast it's spun up, and with all factors being conducive now, or at least most...
Only a 5mph increase in 12 hours? Or a 10 in 24 hours? Maybe due to land interaction, but it's not like it's near the mountains of Hispaniola.
yea its TD 4 now
Unfortunately you'd only have to take a look at west africa and the models to know we got another one coming
hey... weather456... soo what you think about TD4... you think it will make TS by 8PM like I said last night...
I could not find your question,
while it did not make TS status by 5 am, you still were close with TD 4.
My thoughts are with very low shear and warm ssts, only proximity to land would hinder development which is about 36-48 hrs away. This could easily become TS Claudette later today.
I will have a full update on my blog later this morning on all three systems.
LOL ECMWF shows another two storms forming in the Tropical Atlantic over the next 10 days.
Looks like it's moving NW to NNW....right up here....
***reaches for BP meds***
Maybe its my 3am eyes, but is td4 closing off?
Watching frame to frame isnt proper however it appears that the motion is more N than W.
Thoughts?
Actually, it has a mid-level circulation. Check QuikSCAT, no low level circulation. Check CIMSS low-level wind field...no low level circulation. Check pressure readings in the buoys of the GOM...no low level circulation.
Just saw that. It'd be interesting how many more storms we can fit into August before the MJO becomes unfavorable.
Im in Germany for 7 more days so I should miss the activity if anything happens near PBC.
want some of Press's thorazine?
The pass was from a while ago. It is likely now that the system has a closed low.
Looks like it.
NEXRAD Radar
Tampa, Storm Relative Mean Radial Velocity 0.50 Degree Elevation Range 124 NMI
Heck...I may need it.
By 2mb.
Drake.. That was an hour ago...actually may have been 2 hours.. 6:50 UTC is either 1:50 am EST, or 2:50 am EST.. I can't remember if its 4 or 5 hours ahead of EST. Either way it's not an old pass, and yes it has the ability, with such a defined mid-level circulation, to reach the surface very quickly, but it'll still probably take about 6 hours or so, maybe 12.
Throw the lithium on the storm! It'll neutralise the depression...
GN Tex. Don't worry if it goes west you'll hear me scream. ;)
Does that indicate an overall push for quicker development
Excellent radar...moving NNW....
I probably would...If I saw that right you are in Vidor? I'm about 10 minutes away I believe.
Yes we did....hope all is well with you.
The bottom purple is the time of the pass. That was from 8hrs+ ago
OMG A CONFESSION!?!?!?! I better screenshot this...
I'm in Destin, northwest of the depression, and there are easterly winds here, so it's definitely down at the surface. The Navy wouldn't have upgraded it to TD 4 if that wasn't the case.
WS....you're unbelievable....lucky dog?
I'm almost speechless with you.
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