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COMMENTARY

Charting the path, awaiting the wrath of dangerous Dorian

As of this writing Friday afternoon, Dorian has just become a Category 3/Major Hurricane.

Since the atmosphere behaves as a fluid influenced by many factors always in flux, I am going to focus on what are the higher confidence probabilities in Dorian’s development with an understanding there are still uncertainties in the storm’s path, intensity and impacts further out in time next week.

Unfortunately, what is high confidence is very bad news for the northwest Bahamas and for much of densely populated Florida. Here is the National Hurricane Center/NHC track forecast. Please note the dates and time depicted in the cone of uncertainty:

Models and their ensembles are in very good agreement Dorian will continue as a major hurricane and slow in its forward motion as it approaches the Florida east coast later on Monday.

The “M” in the black circles stands for major, meaning at least Category 3. Intensity forecasts are generally less reliable than track forecasts due to extraordinarily complex physics, but this hurricane has everything going for it. There will be less wind shear tearing at its circulation as it moves west or west-northwest. Sea surface temperatures, always warm in late August, are above average for this time of the year. In the legend, everything right of midpoint is above average:

There is obviously plenty of abundant heat energy in the waters along its track.

Some of the highest confidence lies in the slowing forward motion of Dorian. This means more time over the very warm waters before there is land interaction. The actual landfall will be a very slow process (a number of models forecast forward motion of 4 to 5 mph at landfall), meaning much lengthier duration for the storm surge north of the eyewall  to produce its violent destructive flooding, and a much lengthier duration for hurricane and tropical storm force winds. These winds will eventually extend well inland. Possibly worst of all will be the duration for tropical deluges, with forecasts of as much as 3 feet of rain in some locations, but a general range of 6 to 15 inches outside the worst pockets:

As for destructive winds, think of how we react to a single gust of 75 mph in Western New York. Just imagine enduring up to 36 hours of destructive tropical storm and hurricane force winds, with structures unraveling and collapsing under that type of stress. The confidence on this slowing forward motion is high because virtually every model shows very weak steering winds aloft. There is even good agreement in newer private sector modeling, shown in IBM The Weather Company’s MPAS model, courtesy of Dr. Michael Ventrice. (Notice Ventrice’s use of the phrase “stalling track” in his tweet. The tendency to stall shows in still another IBM model he tweeted out, called “Deep Thunder.”)

This tendency toward stalling showed up in Hurricanes Harvey in 2017 and Florence last year, and may be linked to more prevalent blocking patterns tied to arctic warming's weakening of upper level winds. I’m not going to deal with possible warming climate ties to Dorian, since the priority now is the evolution of the storm, with postmortems to follow. Whatever the causes of more frequent stalling, this slow motion is irrefutably the root cause of incredibly destructive flooding.

Confidence is lower on any precise Florida landfall location since the upper level winds will be so weak and diffuse, and because landfall doesn’t come until early next week. The newest run of the European actually has the center still offshore early on Tuesday.

In fact, the European has Dorian still hugging the Florida east coast on Wednesday.

The European had the most southerly track for Dorian back on Wednesday, crossing the Florida peninsula and regenerating out in the eastern Gulf. Now, it is leaning toward recurvature to the northeast, which would pose a major threat to the Carolina coasts later next week.

I tweeted on Aug. 29th a simple reminder that no one model has THE answer, especially in a single model run. As you can see, this sharp shift in the European track forecast much further out in time is a clear indicator of the inevitable increase in track uncertainties further out in time.

Before Dorian gets to that stage 5-7 days out, here is what NHC and most meteorologists are most worried about: “The NHC forecast calls for additional intensification, and Dorian is expected to become an extremely dangerous major hurricane soon with additional strengthening likely as it heads for the northwestern Bahamas and the Florida peninsula.”

This will be the third consecutive year in which a major hurricane makes landfall in the U.S. (Harvey, Michael and now Dorian). That frequency hasn’t happened in 60 years. Every indication we have as of this writing is Dorian will have all the makings of a major natural disaster. I will offer some updates as necessary in the comments section below this article.

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