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Destructive Hurricane Dorian crawls toward East Coast

Don Paul

Extremely dangerous category 4 Dorian came to a virtual stall, as forecast, early on Monday, over Grand Bahama Island. This prolongs the unimaginable agony over that beleaguered location, with top winds of 165 mph in the inner eyewall at landfall there, now at 155 mph. Here is high-resolution NOAA GOES imagery, via the College of DuPage.

For Florida’s east coast, there is one potential positive in this stalling. A blocking ridge of high pressure to Dorian’s north has been keeping the limited forward motion westward, directly toward Florida. Last Wednesday, most models (including the European) were forecasting this motion to continue into and across the state out into the Gulf of Mexico. Shortly afterward, models began to indicate a weakening and shifting of the blocking ridge, along with the approach of a trough of low pressure from the United States.

This development is what has led to most – not all –models predicting a northward turn for Dorian before the center could reach Florida. There has been great uncertainty in just when this right turn would develop. Just a small delay and deviation in the storm track westward would bring a landfall to Florida, and this still cannot be ruled out. However, the hours of stalling are actually giving more time for a weakening in the ridge to the north prior to Dorian’s closest proximity to Florida. This weakening may already be showing up in the shape of the ridge, as seen in this surface analysis.

This possible better news is reflected in the last run of a high-resolution model used by the National Hurricane Center (NHC), called the HWRF. Saturday and Sunday this model, along with the IBM MPAS model, had been indicating a landfall, which would have brought winds in the range of 140-plus mph along with a maximum storm surge to the central and northeast part of the Florida coast. As of this writing, though, this model now keeps the most destructive part of the eyewall offshore.

There is good agreement with another hi-res model, called the HMON at 4 a.m. Wednesday.

Still, just look in the HMON at how close the eyewall is to Cape Canaveral, just to its west. That is why we emphasize how a slight deviation to the west could still result in much more damage. When steering winds aloft are so weak and diffuse, this amount of error in 36-48 hours in the track is not a low probability. The much-improved track forecasts still have a common error of 65 miles 48 hours out.

So, now let’s look at the NHC track forecast and cone of uncertainty issued at 11 a.m. Monday.

I don’t include the center line in the cone because it implies more certainty than actually exists. Note the cone still includes the central and northeast part of the Florida east coast. In recognition of possible track error, NHC has a hurricane warning in effect for the area in red, from Jupiter inlet to the Flagler/Volusia County line and a hurricane watch in pink to the north. In lay turns, their track forecast is “too close for comfort” not to issue the warning.

The best-case scenario still includes damaging, flooding wave action and tropical storm force winds of 39-74 mph. The worst-case scenario brings 74 mph to 100-plus mph winds to the warned area with destructive storm surge in a still slow-moving major hurricane. There would also be a smaller probability of winds somewhat stronger than this upper range with a more direct landfall as intensity forecasts have not improved as much as track forecasts.

There will be gradual, uneven weakening of Dorian during its approach to Florida. Some deeper, cooler bottom waters near the Bahamas will upwell to the surface due to the expanding storm, lessening the supply of heat energy. Wind shear aloft will be to increase at 36 to 48 hours, inducing some modest weakening as well. Even so, the intensity forecast is for top winds of 125 to 130 mph at its closest proximity to Florida (category 3-4), which will produce a major storm surge. A storm surge warning is in effect from Lantana to the Volusia/Brevard County line.

Dorian will finally begin to gradually increase its forward motion as it passes north Florida and recurves more to the northeast, drawing very near or onshore to the Carolina coastlines as a category 2 or 1 hurricane. Mandatory evacuations are already underway in at least coastal counties in those two states due to the high probability of major hurricane impacts.

For those with friends, family or interests in Florida, here are the cautionary words from NHC:

“It cannot be stressed enough that only a small deviation to the left of the NHC forecast could bring the core of the extremely dangerous hurricane onshore of the Florida east coast within the hurricane warning area. In addition, Dorian's wind field is predicted to expand, which would bring hurricane-force winds closer to the east coast of Florida even if the track does change.”

I will provide updates as necessary in the comments section below this article, as well as on Facebook and Twitter.

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