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Tropical Storm Douglas Discussion Number 5
NWS National Hurricane Center Miami FL EP082020
500 AM HST Tue Jul 21 2020
A recent SSMIS microwave pass indicated that Douglas's low-level
center is located very near the head of a broken band of convection
which curls around the southern, western, and northern side of the
circulation. This center is also now embedded beneath a Central
Dense overcast in infrared imagery, near an area of cold
overshooting cloud tops. TAFB and SAB Dvorak classifications have
both risen to T3.5, and Douglas's initial intensity is therefore
raised to 55 kt.
Douglas continues to dip west-southwestward, or 255/13 kt, due to
strong mid-level ridging to its north. A mid- to upper-level low
located northeast of the Hawaiian Islands is forecast to retrograde
westward over the next few days, which will allow the ridge to take
on a more east-west orientation. As a result, Douglas is expected
to turn westward later today and then move west-northwestward
beginning overnight Wednesday into the weekend. The track guidance
all agrees on this scenario, but there are some speed differences,
bookended by slower GFS and HWRF solutions and a faster ECMWF
solution. Overall, however, the new NHC forecast remains very
close to the multi-model consensus aids, and no significant changes
were made compared to the previous forecast, except maybe a slight
northward adjustment on days 4 and 5.
The low-shear, warm sea surface temperature environment within
which Douglas is moving is a recipe for continued strengthening,
potentially at a rapid rate, for the next 48 hours. The intensity
guidance has been trending higher, and the latest SHIPS Rapid
Intensification (RI) indices are highlighting the increased chance
of RI. For example, there is currently a 50/50 shot that Douglas's
winds will increase by 25 kt within the next 24 hours, and a 40-50
percent chance of a 30-kt increase during that period. Based on
this guidance, the new HCCA and Florida State Superensemble
solutions, and the intensity consensus, the NHC intensity forecast
has been increased from the previous cycle and now shows Douglas
becoming a hurricane later today with a higher peak occurring in
about 2 days. Since oceanic heat content falls to zero along
Douglas's path by day 3, some gradual weakening is shown in the
latter stages of the forecast.
FORECAST POSITIONS AND MAX WINDS
INIT 21/1500Z 12.4N 124.2W 55 KT 65 MPH
12H 22/0000Z 12.1N 126.0W 70 KT 80 MPH
24H 22/1200Z 12.1N 128.5W 80 KT 90 MPH
36H 23/0000Z 12.6N 131.0W 85 KT 100 MPH
48H 23/1200Z 13.6N 133.7W 90 KT 105 MPH
60H 24/0000Z 14.9N 136.5W 85 KT 100 MPH
72H 24/1200Z 16.1N 139.4W 75 KT 85 MPH
96H 25/1200Z 18.0N 145.5W 65 KT 75 MPH
120H 26/1200Z 18.5N 151.5W 55 KT 65 MPH
$$
Forecaster Berg
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