Atlantic/2019/05L/Archive/27

Powerful Hurricane Dorian is impressive on satellite imagery this morning, with a well-defined eye surrounded by a thick ring of cloud tops below -60C,. In more recent hours, the storm has become somewhat more squashed latitudinally but retains robust convection and good organization. Areal shear analyses indicate the presence of some light narrow-band upper-shear and upper divergence west of the hurricane, but this is not affecting the storm considerably at this time aside from modest asymmetry and a slightly reduced western periphery. Although the last microwave dataset received at 1127z was not conclusive, visible/infrared satellite imagery and aircraft data from within the storm are indicative of the onset of an eyewall replacement cycle in its early stages. Based on data from both the Air Force Reconnaissance Reserve and NOAA aircraft investigating Dorian, the current intensity has been raised to 130 kt as a blend between dropsonde data, peak SFMR winds of 141 kt, and peak 750 hPa flight-level winds of 141 kt.
The latest motion vector based on the reconnaissance data appears to be approximately 285 degrees at 10 knots. Due to maintenance issues with upper-air in-situ reconnaissance aircraft, it has been difficult to confidently diagnose the steering environment surrounding Dorian. Based on satellite-derived data, Dorian is currently entrenched in a westerly to west-northwesterly flow regime stemming from a 589 dm ridge over Bermuda. This should continue for at least the next day, and perhaps up to two days based on available ensemble guidance. The resulting track up to this juncture should take Dorian close to if not over the northern Bahamas, including Great Abaco and Grand Bahama, as a powerful and life-threatening hurricane. Afterwards, a progressive shortwave off presently over southern Illinois is expected to weaken this ridge somewhat, causing steering currents near Dorian to break down in approximately two days, resulting in an anticipating slowdown and perhaps quasi-stationary stall.
The resulting weakness produces a large amount of uncertainty in the models with regards to where this turn occurs, but tends to favor a northward turn aided by the instability boundary provided by the Florida peninsula and Gulf stream and the shortwave's presence. Early cycle model guidance shifted east a bit more with the 12z suite. Once Dorian makes this turn, the shortwave will depart, allowing either a second eroding shortwave or developing Southern US ridge to fill the vacuum. At present the second shortwave solution seems more likely, allowing Dorian to continue its northeastward recurve. It is prudent to note that while the latest guidance envelope has increased the likelihood of impacts in the Carolinas as well as offshore solutions, while decreasing the likelihood of Florida landfall solutions, the landfalls at all points in the Southeastern United States remain plausible outcomes.
As mentioned earlier, there are tentative signs that an eyewall replacement cycle may be soon occurring. HFIP diagnostic parameters indicate that this will likely occur within a favorable region with relatively light 10 kt deep-layer shear, sea surface temperatures near 29C, and mid-level relative humidity values in the upper 50%. Acknowledging these favorables, the cycle will likely stabilize Dorian's intensity and curb strengthening for throughout today, though the degree of impact on the hurricane's intensity is contingent on the progression of the cycle itself. All parameters remain favorable for continued intensification, though as discussed previously the anticipated slowdown could promote upwelling and thus cool sea surface temperatures to the point of inhibiting the storm, most likely in days 2 and 3. Afterwards, a decrease in surface temperatures and moisture content are expected to weaken the storm further towards the end of the forecast window.

FORECAST MAX WINDS
INIT 31/1500Z 130 KT 150 MPH
12H 31/0000Z 130 KT 150 MPH
24H 01/1200Z 135 KT 155 MPH
36H 01/0000Z 135 KT 155 MPH
48H 02/1200Z 125 KT 145 MPH
72H 03/1200Z 115 KT 130 MPH
96H 04/1200Z 105 KT 120 MPH