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Tropical Storm Dorian Discussion Number   3
NWS National Hurricane Center Miami FL       AL052019
1100 PM AST Sat Aug 24 2019

Dorian's structure hasn't changed substantially since the last
advisory. Although southeasterly shear and surrounding dry air
appear to be limiting convection, the most recent available
microwave imagery showed that the small cyclone is maintaining
well-defined convective banding. The initial intensity is still
35 kt, based primarily on the most recent TAFB Dvorak fix.

Confidence in the intensity forecast is particularly low due to a
number of factors. The small size of Dorian could make it
susceptible to large short-term swings in intensity (up or down).
While SHIPS diagnostics suggest that the wind shear will be below 10
kt for at least the next 72 h, UW-CIMSS shear diagnostics indicate
that the current shear is higher, more like 15-20 kt. And the
intensity guidance spread is also notably large, further decreasing
confidence in the forecast. For now, the NHC intensity forecast has
not been significantly changed, and shows Dorian near hurricane
strength when it approaches the Lesser Antilles in a few days. This
is a little above the intensity consensus and it should be stressed
that it is still too soon to pinpoint potential wind impacts across
those islands, given the large uncertainty in the forecast. The
official forecast then shows Dorian maintaining hurricane strength
across the northeast Caribbean, but it is certainly possible that it
could be weaker, especially given the expected surrounding dry
environment and a possible increase in wind shear forecast by the
GFS and ECMWF models. By the end of the forecast period, the NHC
intensity forecast is very close to HCCA and IVCN.

An ASCAT-B overpass at 0024 UTC revealed that Dorian is moving
slightly faster than previously estimated, now 280/12 kt. Unlike the
intensity guidance, the track models are in quite good agreement on
the track of Dorian. The tropical storm should continue moving
westward to west-northwestward at a similar forward speed, steered
primarily by a mid-level ridge stretching across most of the central
Atlantic. The NHC forecast is nearly on top of the previous advisory
and remains very near the TVCN and HCCA consensus aids.

Key Messages:
1. Dorian is forecast to strengthen and could be near hurricane
strength when it approaches the Lesser Antilles on Tuesday.

2. It is too soon to determine the specific timing or magnitude of
impacts in the Lesser Antilles, but tropical storm or hurricane
watches will likely be needed for a portion of the islands on
Sunday.


FORECAST POSITIONS AND MAX WINDS

INIT  25/0300Z 10.9N  50.4W   35 KT  40 MPH
 12H  25/1200Z 11.2N  52.0W   40 KT  45 MPH
 24H  26/0000Z 11.7N  54.1W   45 KT  50 MPH
 36H  26/1200Z 12.5N  56.2W   50 KT  60 MPH
 48H  27/0000Z 13.2N  58.2W   55 KT  65 MPH
 72H  28/0000Z 15.0N  62.3W   65 KT  75 MPH
 96H  29/0000Z 17.0N  66.5W   70 KT  80 MPH
120H  30/0000Z 19.0N  70.0W   55 KT  65 MPH...INLAND

$$
Forecaster Zelinsky

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