[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 022055
TCDAT1

HURRICANE JOAQUIN DISCUSSION NUMBER  20
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL112015
500 PM EDT FRI OCT 02 2015

Satellite imagery and reports from an Air Force Reserve Hurricane
Hunter aircraft indicate that Joaquin has weakened a little since
the last advisory, with the central pressure rising to 942 mb.
Based on this, the initial intensity is decreased to 110 kt.
Subsequent observations from San Salvador Island and dropsondes from
a NASA aircraft suggest the pressure is still near 942 mb.  While
the hurricane continues to produce cold cloud tops in the eyewall,
the convective pattern currently looks ragged in infrared imagery,
and only occasional hints of a eye are apparent in visible imagery.

The initial motion is now 360/6.  Water vapor imagery shows a mid-
to upper-level ridge to the north and northeast of the hurricane,
while a deep-layer trough and associated surface front are located
over the southeastern United States.  This system is forecast to
move slowly eastward with a non-tropical low forming along the
front during the next couple of days.  While this occurs, a mid- to
upper-level low currently centered near 30N 64W should move
west-northwestward to the north of Joaquin.  These developments
should steer Joaquin northward for the next few hours, followed by
a turn toward the northeast.  The track guidance is now in good
agreement that Joaquin will move generally northeastward between
the United States and Bermuda, with a short-lived northward turn in
the 48-72 hour period.  Eventually, the cyclone is expected to
move into the westerlies and move quickly east-northeastward across
the North Atlantic.  The new forecast track is similar to the
previous forecast and now lies near the consensus models.

Joaquin is forecast to remain in an environment of light vertical
wind shear for another 12-24 hours or so, and during this time some
fluctuations in intensity are possible. After 24 hours, the shear is
forecast to increase, which should start a steady weakening.
Extratropical transition is expected to begin around 96 hours and be
complete by 120 hours. Overall, the new intensity forecast is an
update of the previous advisory and lies near the intensity
consensus.


KEY MESSAGES:

1.  Hurricane conditions over portions of the Bahamas should
continue for several more hours.

2.  Swells from a hurricane moving even far offshore of the U.S.
east coast can still cause life-threatening surf and rip-current
conditions.  Please see products from your local National Weather
Service forecast office.  For information on the heavy rains
occurring along the U.S. Atlantic states that are mostly unrelated
to Hurricane Joaquin, please see products from the NWS Weather
Prediction Center and your local forecast office.

3. Since the direct threat of hurricane conditions to land areas
is diminishing significantly, this will be the last set of key
messages unless the threat increases.


FORECAST POSITIONS AND MAX WINDS

INIT  02/2100Z 24.1N  74.7W  110 KT 125 MPH
 12H  03/0600Z 25.1N  73.9W  110 KT 125 MPH
 24H  03/1800Z 26.9N  72.1W  105 KT 120 MPH
 36H  04/0600Z 29.2N  70.0W  100 KT 115 MPH
 48H  04/1800Z 31.7N  68.7W   90 KT 105 MPH
 72H  05/1800Z 36.5N  67.0W   75 KT  85 MPH
 96H  06/1800Z 40.5N  60.5W   65 KT  75 MPH
120H  07/1800Z 45.0N  46.0W   55 KT  65 MPH...POST-TROP/EXTRATROP

$$
Forecaster Beven
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