03 July 2021

Elsa weakens as it approaches Cuba

Elsa now holds the record as the fastest-moving hurricane in the tropics, during the reliable weather satellite era.  It set that record at 27 mph (beating Hurricane Debby in 2000), but it broke its own record when the forward motion increased to 31 mph on Saturday morning. Records aside, that rapid forward motion actually introduces vertical wind shear across it, which has played a big role in Elsa's weakening on Saturday. 

As of the 5pm EDT advisory, Elsa is a tropical storm with peak winds of 70 mph, and it's racing toward the west-northwest at 28 mph. In addition to the self-induced wind shear, it is also really close to the mountainous southern coast of Haiti.  That combination has taken its toll on the storm's structure, and the upcoming trek across Cuba will be another hit.  Watches and warnings are plastered over Hispaniola, Jamaica, and Cuba, and now the Florida Keys too.

The first tropical storm watches should be issued for more of south Florida tonight, but we already have the routine HTI (Hurricane Threats and Impacts) graphics which break the risks down by the four major hazards associated with tropical cyclones: wind, rain, storm surge, and tornadoes.  The "cone of uncertainty" is overlaid in blue for reference. Always remember that the cone IS NOT an impacts cone (Cone Refresher).

The forecast is still tricky because of the land interaction; that's always a challenge for models and human forecasters alike.  But assuming that it emerges even remotely intact, it is likely to bring wet and stormy conditions to south Florida starting on Monday.  Based on the latest NHC forecast, tropical storm conditions could begin in south Florida midday Monday, as well as the onset of several inches of rain.  It looks very likely that the west coast of the peninsula will experience worse conditions than the east coast (stronger winds, heavier rain, and more storm surge), but folks along the east coast need to be prepared for some stormy weather from midday Monday through Tuesday evening.

One other tidbit that I dug up on Friday afternoon is that there has only been a hurricane in the eastern Caribbean before mid-July in two other years: 1933 and 2005.  Ominously, those two years are the record-holders for the highest ACE (Accumulated Cyclone Energy) in a season.

For those who like to keep track of the ACE as the season progresses, 2021 is now at 293% of average, using the past fifty years as the baseline for the average.  The last season that was so high by this date was 2012.

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