03 September 2019

The unimaginable, again: Major Hurricane Dorian still stationary over Bahamas

Today's post will essentially be a copy of yesterday's. While that may seem like laziness, it's actually to prove a point: Dorian has moved just a few miles in the past day, and it's a still a major hurricane sitting over Grand Bahama.  Truly unimaginable.

Dorian has weakened a bit as it sits in place over the northwestern Bahamas, and as of 8am EDT on Tuesday has sustained winds of 120 mph (Category 3) -- it is still an extremely strong and dangerous major hurricane (defined to be Category 3+).  It is centered 105 miles east of West Palm Beach FL, and the tropical storm force winds extend an average of 140 miles from the center (hurricane force winds extend an average of 40 miles from the center).

Hurricane warnings remain in effect for the northern Bahamas as well as the central and northern Florida coast. The latest various tropical storm, storm surge, and hurricane watches and warnings can be found on the NHC website. As of 8am EDT on Tuesday, the motion in the NHC advisory is given as northwest at 1 mph.  A person typically *walks* at 3 mph.

A more convincing northward turn is forecast to begin later on Tuesday.  If we look at the history of NHC's 5-day track forecasts, we can see the places where Dorian didn't behave quite as expected: eastern Caribbean and northern Bahamas. The thick black line is the observed location, and the thin colored lines are each of the track forecasts. But, in fairness, the forecasts were within the typical margin of error.
The threat to the central and northern Florida coast is still extreme, and the eastern parts of GA, SC, and NC also need to be preparing for a major impact, including significant storm surge.  The HTI (Hurricane Threats & Impacts) graphics break down the four major hurricane hazards: wind, surge, rain, and tornadoes:
Dorian is expected to remain a slow-mover until Wednesday morning, but is already beginning a northward drift. Of course, just how close Dorian gets to the coastline is critical to impacts like wind and storm surge. It is an extremely serious threat and easily within the bounds of normal forecast error. Do not focus on the exact track or the edge of the cone -- neither of them are designed to show impacts. We can monitor the position, eyewall structure, and rainbands from several long, updating radar loops at http://bmcnoldy.rsmas.miami.edu/tropics/radar/.  For example, this one from Miami begins on Sunday morning and as of this post, ends at 8:30am EDT on Tuesday:

From the latest 50-member European model ensemble, none of the members make landfall south of Cape Canaveral, 3 show a landfall north of Cape Canaveral, while the remaining 94% remain either just offshore or well offshore.  The tracks shown here are only plotted out to 3 days. Keep in mind that any of these tracks bring dangerous storm surge and coastal flooding to northern FL, GA, SC, and NC, and the possibility of heavy rain and strong gusty winds.

Other than Dorian, the Atlantic looks like early September: busy! There is a low near Bermuda, two off the coast of Africa, and one in the western Gulf of Mexico.  The one in the Gulf of Mexico, which is quite close to land, is forecast to intensify into a tropical depression or tropical storm today or tomorrow and track west into Mexico.  The next name is Fernand.

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