Dorian becomes a powerful category 4 hurricane with 145 mph sustained winds

Hurricane warnings in effect for the northern Bahamas


A rightward guidance trend yesterday and overnight suggests an increasing threat for impacts in GA, SC, and NC.
Dorian is a well developed powerful hurricane with a clearly defined 12-15nm wide eye embedded within a ring of deep convective storms.
The western side of the system may be ingesting some dry air and there may be a hint at weak shear as the western eyewall is more narrow in that area compared to the eastern side of the storm.
The last USAF mission recorded significant pressure falls yesterday from 970mb in the morning to 946mb in the evening indicating rapid intensification with maximum sustained wind speeds increasing from 110mph yesterday morning to 145mph this morning.
A new plane will be within Dorian shortly, but based on the satellite images this morning it appears Dorian is likely about the same intensity as when the last plane departed.


There has been some adjustment of the global track guidance and official NHC forecast to the right (east) overnight. Dorian has turned toward the WNW and this motion with a turn toward the west will continue for the next 24-36 hours bringing the core of Dorian into the northern Bahama Islands.
The forward speed will slow and it is possible that Dorian stalls over the northern Bahamas, this is in response to the sub-tropical ridge north of the hurricane weakening and breaking down on its westward flank as a short wave trough moves across the Great Lakes into the NE US.
This trough may be strong enough to grab Dorian and turn the hurricane NNW/N offshore the east FL coast and then a turn to the NNE off the SE US coast. Very small scale changes in the steering flow with Dorian by Monday and Tuesday could result in a landfall over eastern FL or the system remaining offshore.
Direct impacts from Dorian are now possible into GA, SC, and NC based on the latest trends, but the eastern coast of FL is still within the error cone of the NHC track and many of the global model ensemble tracks still show direct impacts to the FL east coast. Given the collapse of defined steering currents over the northern Bahamas, uncertainty as to when Dorian turns toward the north is high.


Dorian is a powerful hurricane in an environment favorable for continued intensification. Powerful hurricanes in such environments tend to see intensity changes reflective of eyewall replacement cycles with a decrease in intensity as a new outer eyewall forms and then an increase in intensity as that outer eyewall contracts inward and the old inner eyewall dissolves.
The most important factors of an eyewall replacement cycle is that the wind field tends to expand outward during such periods.
Dorian is expected to impact the northern Bahamas as a powerful category 4 hurricane. As Dorian begins to turn NNW/N near the FL coast the interaction of the circulation with land and some increasing vertical wind shear will likely help weaken the system as it moves toward the SE US coast.
Should Dorian make landfall in FL, the intensity forecast for the longer ranges is too high and would need to be reduced.


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