02 September 2011

Katia hanging on, TD13 forms in Gulf

Katia actually went against model guidance again and weakened a bit to a strong tropical storm yesterday afternoon, but has since reintensified to a minimal hurricane (65kts, 991mb).  The vertical shear was quite a bit stronger than forecast, and it definitely took a toll on the storm.  However, with shear dropping from 20kts to 10kts over the next couple of days, Katia should be able to resume the previous strengthening trend.
The official forecast calls for gradual intensification to 100kts (Cat 3) over the next 5 days as it heads WNW... with a 5-day (Wednesday) position located about 500 miles north of Puerto Rico.  The long-term future is still too uncertain as to whether it will recurve before reaching the US east coast or not, but extended-range models generally indicate a safe recurvature.  Certainly something to keep a very close eye on anywhere along the east coast though.

The disturbance that I first mentioned on Tuesday has been upgraded to TD13, and is not far from becoming Tropical Storm Lee.  This disturbance was way back by the Lesser Antilles on Aug 25, so it's been "on the radar" for a week now.  It is organizing very quickly now that the vertical shear is relaxing -- from 25kts to 5kts over the next 24 hours.  The intensity is 30kts, it's centered just 190 miles southwest of New Orleans, it's nearly stationary, and the outer rainbands are already onshore.
Tropical Storm warnings are up for the entire LA and MS coast... the latest forecast track, watches, and warnings can always be found at http://www.nhc.noaa.gov/storm_graphics/AT13/refresh/AL1311W5+gif/145613W_sm.gif

The 5-day accumulated precipitation forecast from HPC is still very ominous for the southeast, with 1-2 feet of rain possible over southern LA and MS.  You can watch the regional radar loop showing the extent of the rainfall at http://radar.weather.gov/Conus/southmissvly_loop.php 

This flooding rain will be combined with perhaps multiple days of tropical storm force winds, and I wouldn't be surprised at all if some evacuations were ordered for New Orleans, Biloxi, Mobile, Pensacola, and other urban flood-prone cities in the area (as well as offshore oil rigs).  If you or someone you know is down there, keep a close eye and ear to the local tv and radio stations this weekend.

Finally, the circulation that was north of Bermuda yesterday has not moved much at all, but is actually even more sheared than it was... making any development unlikely.  What convection there is in association with this system is displaced far to the northeast, and while the SSTs are fairly high now (28C), they will plummet to 22C within a day as it moves to the northeast.

Please visit my tropical Atlantic headquarters.

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