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Tropical Storm Harvey Forecast Discussion (Text)


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WTNT44 KNHC 190233
TCDAT4

Tropical Storm Harvey Discussion Number   7
NWS National Hurricane Center Miami FL       AL092017
1100 PM AST Fri Aug 18 2017

Microwave and conventional geostationary satellite images indicate
that Harvey's center is still displaced to the east of a persistent
cluster of deep convection due to about 15 kt of northeasterly
shear.  With no notable changes in the cyclone's structure since
the last advisory, the maximum wind estimate remains 35 kt, which
is in line with the latest Dvorak CI numbers.

Recent microwave fixes suggest that Harvey's center may have slowed
down or wobbled northward temporarily, and the 12-hour motion
estimate is a slightly slower 275/16 kt.  A low- to mid-level ridge
extending across the western Atlantic should keep Harvey on a swift
westward course across the Caribbean Sea for the next 48 hours.
Once Harvey moves into the northwestern Caribbean Sea by 72 hours,
it will reach the western edge of the ridge, and it will likely
slow down and gain some latitude due to a cut-off low over the
northwestern Gulf of Mexico.  Although the track guidance envelope
has shifted slightly northward on this cycle, especially around the
72-hour period, there are no significant changes from six hours ago.

Northeasterly or northerly shear is forecast to continue for the
next 36 hours or so, which should prevent significant strengthening
while Harvey moves westward across the eastern and central
Caribbean Sea.  By 48 hours, the vertical shear over the cyclone
drops drastically, but the system's fast motion could still
limit the amount of intensification that will occur.  The best
opportunity for strengthening would likely be around day 3 when
Harvey begins to slow down as it approaches Belize and the Yucatan
Peninsula.  The updated NHC intensity forecast is the same as the
previous one during the first 48 hours, and it was nudged a little
lower at 72 hours to fall closer to the HFIP Corrected Consensus
(HCCA) model and the ICON intensity consensus.  A lot of
uncertainty remains, however, since models like SHIPS and HWRF
bring Harvey near or to hurricane intensity before it reaches land
while the GFS and ECMWF continue to weaken the circulation while it
moves across the Caribbean Sea.

FORECAST POSITIONS AND MAX WINDS

INIT  19/0300Z 13.7N  64.1W   35 KT  40 MPH
 12H  19/1200Z 14.0N  66.8W   35 KT  40 MPH
 24H  20/0000Z 14.3N  70.4W   40 KT  45 MPH
 36H  20/1200Z 14.5N  74.3W   40 KT  45 MPH
 48H  21/0000Z 14.8N  78.1W   45 KT  50 MPH
 72H  22/0000Z 16.5N  84.7W   55 KT  65 MPH
 96H  23/0000Z 18.0N  89.5W   45 KT  50 MPH...INLAND
120H  24/0000Z 19.0N  92.5W   40 KT  45 MPH...OVER WATER

$$
Forecaster Berg


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Page last modified: Saturday, 19-Aug-2017 02:34:10 UTC