29 August 2019

Hurricane Dorian expected to intensify as it heads toward Florida

On Wednesday, Dorian did end up tracking far enough east of Puerto Rico that the storm's circulation was not affected at all... in fact, it strengthened into the season's second hurricane right as it passed by the island.  As of 8am EDT on Thursday, it is a Category 1 hurricane with 85 mph sustained winds and is centered 150 miles north of Puerto Rico, and 1000 miles southeast of Cape Canaveral FL.  Tropical storm force winds only extend an average of 60 miles from the center, but storms typically gradually expand with time.

All environmental indicators suggest that Dorian will strengthen substantially in the next few days before reaching land. While there's a small probability that the storm turns north before reaching the southeast U.S. coast, by far the most probable outcome is a landfall along the Florida peninsula. The European (ECMWF) and American (GFS) models and their ensembles continue to indicate a spread spanning all of Florida and up into the Carolinas and some are even offshore.  In other words: be prepared.  The most probable area as of now is central Florida though.

Track density from the ECMWF ensemble (left) and the GFS ensemble (right). In both maps, the individual ensemble members are the thin gray lines and the NHC forecast is the thick black line.  On the left, the ensemble mean is not shown but the deterministic forecast is the red line.  On the right, the ensemble mean is the red line, and the deterministic forecast is the green line.  Graphics courtesy of Brian Tang at UAlbany. 
Regarding wind impacts, the timing of the onset of tropical storm force winds is what's important, because all outdoor work and preparation should be completed by then. As of now, that could be as early as Saturday evening along the east coast of Florida.  Landfall, which is when the center crosses a coastline, would most likely be Monday morning, but the timing has uncertainty too.  It could be at least a Category 3 hurricane when it makes landfall.  The irony of a Florida Labor Day Hurricane is not lost on us (for anyone who doesn't know, the Labor Day Hurricane of 1935 is still the most intense landfalling hurricane not just in Florida, but in the entire US).

Based on this, we could start seeing tropical storm and hurricane watches be issued for Florida tonight or Friday morning.  You should always consult the NHC website for the most current information.

Suppose Dorian is tracking due west when it hits the Florida peninsula. Not only is there the first impact along the east coast, but shortly after, the west coast of Florida will also get a hurricane, complete with rain, wind, and storm surge.  The Florida peninsula is flat and narrow and is barely an obstacle for hurricanes.  Then, you have a hurricane in the Gulf of Mexico which will inevitably hit somewhere else.

A hurricane hazard to never overlook is rain... and Dorian is no exception. Although this depends a bit on the exact track, heavy flooding rain occurs for hundreds of miles away from the storm center. This map shows the forecast rainfalls over the coming week.

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