Tropical storm Andrea forms, strengthens, and targets Florida, East Coast

June 6, 2013

Since forming Wednesday afternoon, tropical storm Andrea’s appearance has grown much more impressive on satellite, signaling a strengthening storm.  As of 11 a.m. EDT, Andrea’s peak winds have increased to 60 mph.  But copious rains will be Andrea’s most significant impact, as it charges up the East Coast.


Radar, visible satellite, and enhanced infrared satellite images of Andrea at 8:45am EDT today. (Weather Underground, NOAA)

The storm’s center is presently located 110 miles west of Tampa, and its outer bands are lashing the Florida peninsula and south Georgia with heavy rains and gusty winds. Radar imagery shows a nascent eyewall coming into view and approaching the Florida coast.  (To help track the coverage and structure of the rainfall, see the long radar loops available I’ve made available).

Flood watches cover huge parts of Florida, Georgia, South Carolina, and North Carolina. These will inevitably be extended northward with time.

In addition to the heavy rain threat, tornadoes are also possible within a few hundred miles of the storm’s center, mainly to its east.  Presently, the majority of the Florida peninsula is under a tornado watch. Six tornadoes have already touched in the Sunshine State, says The Weather Channel’s Greg Forbes.

Sustained tropical storm winds of 40-60 mph, with some locally higher gusts, are possible near the center of Andrea’s track when it makes landfall. These peak winds will quickly decrease into the 20-40 mph range after the storm moves over land and will tend to focus east of its track.

Some minor storm surge in the 2-4 feet range is likely along the western Florida coast, south of the track, decreasing to around 1-2 feet south of the Chesapeake Bay and 1 foot to the north.


Andrea hazard summary from National Weather Service

The National Weather Service website is a great place to find up-to-the-minute watches and warnings.

This storm formed from the disturbance that I mentioned in a blog post last Friday, and models (most notably, GFS) have been consistently predicting the scenario that is now playing out.  The timing, landfall location, intensity, and structure of Andrea have all been predicted with impressive accuracy by global models for several days prior to its official formation.

Today, the NHC forecast and models are in excellent agreement on the future track of Andrea… with a landfall expected later this afternoon near Perry, FL (between Tallahassee and Gainesville), then racing northeast over the Carolinas during the first half of Friday,  eastern Virginia and the Delmarva peninsula later on Friday, then finally offshore and toward Nova Scotia on Saturday.

Andrea is unlikely to reach hurricane intensity.  The official track forecast with the latest tropical storm warnings is shown above (for a refresher on what the forecast cone is and isn’t, see “Atlantic hurricane season 2013: What’s new and what should we expect?”).

Of course, given the storm’s sprawling plume of moisture, conditions deteriorate many hours before the center arrives, so if you expect the center to be near your area on Friday evening, wind and rain will start picking up by Friday morning, if not sooner.

Forecast rainfall totals over the next three days are generally in the 2-5” range over nearly all of Florida, then eastern parts of all of the coastal states.  Locally heavier accumulations are certainly possible, and bring with them the risk of flooding and flash flooding.

Three-day rainfall forecast. (WPC)
Three-day rainfall forecast. (WPC)

Generally, 1-3 inches of rain are forecast for the Washington, D.C. area with the highest totals east of the city.  East of the Chesapeake Bay, 2-4 inches are possible, with locally higher amounts. More detailed Washington, D.C. specific impacts will be posted this afternoon.

Elsewhere in the Atlantic basin, the easterly wave that I discussed last Friday is still a very interesting feature, and is located about 1000 miles east of the Lesser Antilles.  The upper-level winds are too strong for any real development, and they are not expected to improve much in the foreseeable future.  However, I will continue to monitor it as it heads west then northwest across the deep tropics.

* Brian McNoldy is a senior researcher at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science.

Video overview of Andrea from Associated Press

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Kevin Ambrose · June 6, 2013