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Tropical Storm JOAQUIN


500 AM EDT WED SEP 30 2015

The coldest convective cloud tops are located to the east of the
estimated center position, but there have been hints of an eye in
infrared imagery overnight. Based on a blend of the latest Dvorak
estimates from TAFB and SAB, the initial intensity remains 60 kt. An
Air Force Reserve Hurricane Hunter aircraft is on its way to
investigate Joaquin this morning. Conditions are expected to be
conducive for intensification during the next few days, with Joaquin
moving over very warm waters with shear steadily decreasing. The
hurricane intensity guidance and the latest runs of the GFS, UKMET,
and ECMWF all show Joaquin intensifying, and in fact, the global
models show the central pressure in the 950s or lower. The NHC
forecast is near the latest intensity model consensus, and has
Joaquin peaking in 72 hours. After that time, the cyclone will be
moving into a higher shear environment and over cooler waters, which
should result in slow weakening.

Joaquin continues to move west-southwestward under the influence of
a short-wave ridge to its north, and the initial motion estimate is
245/05. This motion should continue for the next 24 hours, and
Joaquin is expected to then turn slowly westward as the ridge
weakens on Thursday. The UKMET and ECMWF continue to show Joaquin
moving farther southwestward into the central Bahamas than the rest
of the guidance. The new NHC track in the short range is a little
south of the previous one, but north of the UKMET/ECMWF solution.
Given this new forecast, the government of the Bahamas has issued a
Hurricane Warning for the central Bahamas and a Hurricane Watch for
part of the northwestern Bahamas.

After 36 hours, Joaquin is forecast to turn northwestward and then
northward as it interacts with a deep-layer trough that cuts off
over the southeastern United States in about 3 days. Much of the
deterministic guidance shows Joaquin turning northwestward
toward the mid-Atlantic coast by days 4 and 5. However, the ECMWF
continues to show an offshore solution with a track west of Bermuda,
but has shifted to the left this cycle by about 150 miles at day 5.
While the overall synoptic pattern is similar between the models,
the eventual track of Joaquin appears sensitive to just how far
southwest it moves in the first 36 to 48 hours and how this affect
the eventual interaction with the upper-level low. The GFS, HWRF,
and GFDL show a sharp turn back to toward the coast in 4 days, while
the ECMWF is slower to bring Joaquin northward and ejects the
cyclone toward the northeast. The UKMET is between those two
scenarios with a broader turn back toward the coast by day 5. There
is still ensemble support for a wide range of solutions, so
confidence in any deterministic model solution remains quite low.
The NHC track has been nudged a little to the left this cycle to
reflect the westward shift in the guidance, but lies on the eastern
side of the guidance envelope given the ECMWF solution.

Confidence in the details of the track forecast late in the period
remains very low, since the environmental steering currents are
complex and not being handled in a consistent manner by the models.
Given that a wide range of outcomes is possible, it is too soon to
say what impacts, if any, Joaquin will have on the United States.


INIT  30/0900Z 25.4N  72.5W   60 KT  70 MPH
 12H  30/1800Z 25.1N  73.0W   70 KT  80 MPH
 24H  01/0600Z 24.7N  73.8W   75 KT  85 MPH
 36H  01/1800Z 24.7N  74.5W   80 KT  90 MPH
 48H  02/0600Z 25.2N  74.7W   90 KT 105 MPH
 72H  03/0600Z 28.3N  73.5W   95 KT 110 MPH
 96H  04/0600Z 33.0N  73.0W   85 KT 100 MPH
120H  05/0600Z 37.0N  73.5W   80 KT  90 MPH

Forecaster Brennan