Atlantic/2019/05L/Archive/29

Dorian has exploded into a Category 5 hurricane. Data from two reconnaissance aircraft indicate an extremely strong tropical cyclone, with peak flight-level winds of 152kt and numerous SFMR values between 140-150kt. In addition, a dropsonde that rotated into the southwestern eyewall measured an instantaneous gust of 155kt, with a mean wind of 151kt throughout the lowest 150m of the atmosphere. Conventional satellite depicts a beautiful monster, with a ring of -70C convection encircling a symmetrical and very warm eye. A blend of the aforementioned data supports upping the initial intensity to 145kt. There have now been Category 5 hurricanes recorded in the Atlantic each of the past four years, an occurrence never seen before in the reliable tropical cyclone database.
It seems dangerous to suggest Dorian will not intensify further given how the tropical cyclone has performed so far. However, it is already above the calculated maximum potential intensity, and so at some point the storm has to level off. That being said, low wind shear, increasing 700-500 relative humidity values, and rising oceanic heat content should promote an extremely powerful hurricane over the coming days. A series of microwave passes from around 21z showed no evidence of an eyewall replacement cycle. One potential theory for this lack of internal structural changes is a mass of dry air outside the hurricane's core to the north, limiting spiral banding that eventually morphs into a secondary eyewall. Thus, the only negative factor over the next 3 days may be cold water upwelling as Dorian slows to a crawl over the northwestern Bahamas. Even then, this solution is mainly supported by the ECMWF, with other models suggesting Dorian may move quickly enough for this factor to be insignificant. This is especially true given Dorian's small radius of hurricane- and even tropical storm-force winds. After day 3, the system should finally succumb to dry air entrainment from the United States, increasing upper-level winds, and perhaps land interaction.
Fixes from the recon plane indicate that Dorian is moving a hair north of due west. This motion should continue for the next 48 to 60 hours before Dorian begins to curve more poleward as high pressure off the Southeast United States breaks down by the influence of an approaching upper-level trough. One noteworthy change in 18z guidance was a shift toward the south and west, the byproduct of a stronger Atlantic ridge than previously modeled. This change was facilitated by the injection of dropsonde data into the guidance. However, this was only a partial data input, with more dropsonde data expected for the 0z cycle. While the chances of a Florida landfall have decreased over the past few days, we may be witnessing a shift back toward the state, or at least close enough that significant effects occur even if the center does not move ashore. This shift is also important for the Carolinas, as any deviations from current expectations could send the hurricane into North Carolina. Regardless, Dorian is expected to track directly through the northwestern Bahamas, likely delivering a catastrophic blow there. The Southeast United States remains at significant risk from this powerful hurricane.
FORECAST MAX WINDS
INIT 01/0300Z 145 KT 165 MPH
12H 01/1200Z 145 KT 165 MPH
24H 02/0000Z 140 KT 160 MPH
36H 02/1200Z 135 KT 155 MPH
48H 03/0000Z 130 KT 150 MPH
72H 04/0000Z 120 KT 140 MPH
96H 05/0000Z 105 KT 120 MPH