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Tropical storm Karen forms, hurricane watches issued for Gulf coast

Aircraft reconnaissance has found that the disturbance in the southern Gulf of Mexico has intensified to a tropical storm: Karen.  Tropical storm and hurricane watches are now in effect for a section of northern Gulf coast.

Cities under the hurricane watch include Biloxi,  Mobile, Panama City, and Pensacola.  New Orleans is in the tropical storm watch area.  Tropical storm conditions could begin in all of these areas as soon as late Friday.

Satellite image of Tropical Storm Karen in the Yucatan Channel. (NASA)
Satellite image of Tropical Storm Karen in the Yucatan Channel. (NASA)

Link: Hurricane Tracker

Maximum sustained winds are already up to 60 mph, but it would be incorrect to say that it rapidly intensified or caught forecasters off-guard.  The disturbance has had aircraft probing it fairly regularly, and while tropical storm force winds have been found for a while now, there was no evidence of a closed surface circulation – a key criteria for any tropical cyclone.  That missing component has now been found, and hence, it’s a moderate tropical storm in its first advisory.

As almost every model predicted, it did indeed become a tropical storm by Thursday morning. This is an excellent success case in intensity forecasting, especially for a system that wasn’t even a numbered storm yet.  The intensity forecast over the next three days will be very important too as it heads for the coast.

As impressive as it may look now, it has just a short window to intensify further before environmental conditions turn more hostile.  The combination of deep dry air and vertical wind shear that I mentioned yesterday are still in its future… about two days away at best.  That’s not to say that it couldn’t become a minimal hurricane in the meantime, but it will not become a serious threat to the northern Gulf as a major hurricane.

The National Hurricane Center and most models are now converging on a landfall near Mobile (+/- 125 miles or so) on Saturday as a strong tropical storm.  The current official track as well as the watches and warnings are shown below, but you can always (yes, even during a partial federal government shutdown) find the latest information on the National Hurricane Center website.

NHC forecast track, cone of uncertainty, and watches/warnings as of 9am EDT. (NOAA)
NHC forecast track, cone of uncertainty, and watches/warnings as of 9am EDT. (NOAA)

A long swath of heavy rain is expected along Karen’s track over the next several days, with 6-8″ possible from eastern Louisiana over to the western Florida panhandle, and several inches from Florida all the way up to Maine.

An interaction with a mid-latitude cold front (or trough) will enhance rainfall potential and amount, so by early next week, the rain coverage will be much more smeared out than it would be if it were just a tropical cyclone.  Rain associated with Karen would reach the D.C. area during the day on Monday… depending on the track.

Six-day total accumulated rainfall from this morning's GFS model run. The swath of heaviest rain will migrate as Karen's track varies in each model run... also, global models are not reputed to be excellent at forecasting exact precipitation amounts. (tropicaltidbits.com)
Six-day total accumulated rainfall from this morning’s GFS model run. The swath of heaviest rain will migrate as Karen’s track varies in each model run… also, global models are not reputed to be excellent at forecasting exact precipitation amounts. (tropicaltidbits.com)

We will be watching this closely, so stay tuned for updates on the tropical storm and for updates on its potential impacts on the D.C. area.

Related: Will Karen dump heavy rain on Washington, D.C.?

Brian McNoldy works in cyclone research at the University of Miami’s world-renowned Rosenstiel School of Marine and Atmospheric Science (RSMAS). His website hosted at RSMAS is also quite popular during hurricane season.
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