[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 010849
TCDAT1

HURRICANE JOAQUIN DISCUSSION NUMBER  14
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL112015
500 AM EDT THU OCT 01 2015

Data from the last aircraft mission indicated the Joaquin had
strengthened a little more, and the intensity of 105 kt is supported
by flight-level, SFMR, and dropsonde data from the plane. The
central pressure of 948 mb is based on a dropsonde that measured 950
mb with 20 kt of wind. The satellite presentation of the hurricane
continues to gradually improve, with cold tops expanding near and
west of the center, although the eye is not yet apparent in infrared
imagery. Another hurricane hunter aircraft will be investigating
Joaquin later this morning.

Joaquin is expected to intensify a little more in the next 12 to 24
hours while over very warm waters and with decreasing vertical
shear. After that time, there could be some fluctuations in
intensity due to eyewall replacement cycles and perhaps some
upwelling of cold waters due to the slow motion of the hurricane.
After 48 hours, cooler SSTs and increasing shear should result in
gradual weakening as Joaquin moves northward. The new NHC intensity
forecast is similar to the previous one and close to the HWRF
through 24 hours. After that time, the NHC prediction is above the
intensity consensus since the official forecast keeps the cyclone
offshore, while the remainder of the intensity guidance shows
weakening due to decay over land.

The initial motion of the hurricane is still toward the southwest
or 230/04 under the influence of a narrow ridge to the north. A
slow motion with a bending of the track toward the west and then
the west-northwest is expected during the next 24 hours as the
ridge weakens. During this time the NHC track has been adjusted
southward following the latest trend in the guidance. The slow
motion of Joaquin will mean a prolonged period of hurricane
conditions in portions of the central Bahamas, along with very heavy
rain and storm surge.

By 36 hours, Joaquin should begin to move faster toward the north as
it comes under the influence of a deep-layer trough that cuts off
over the southeastern United States. There have been big changes in
some of the track guidance overnight, perhaps due to data from the
synoptic surveillance mission flown by the NOAA G-IV jet for the 00Z
model cycle. In particular, the GFS and UKMET have shifted eastward
by several hundred miles in 3 to 4 days relative to their previous
solutions. Overall for this cycle there has been a spreading out of
the guidance envelope beyond 2 days, with a wide range of solutions
shown. The HWRF and GFDL are the fastest to bring Joaquin north out
of the Bahamas and still show a sharp westward turn taking the
cyclone inland over the Carolinas in 3 to 4 days. The GFS has
trended slower coming out of the Bahamas and now shows a track
toward Long Island and southern New England in 5 days, with the
UKMET farther offshore. The latest ECMWF is still the slowest and
farthest east with a track just west of Bermuda in 4 to 5 days.
Given the large shift in some of the guidance, the NHC track has
been adjusted just a little to the east and slower at days 3 through
5, and now lies on the left side of the multi-model consensus and
left of the GFS, UKMET and ECMWF solutions. Confidence remains very
low in the eventual track of Joaquin and any potential impacts for
the United States, and further adjustments to the NHC track may be
needed later today.

KEY MESSAGES:

1.  Preparations to protect life and property in the central Bahamas
should be complete.  The slow motion of Joaquin during the next 24
to 36 hours will bring a prolonged period of hurricane force winds,
storm surge, and very heavy rainfall to those islands.

2.  Confidence in the details of the forecast after 72 hours remains
low, as there have been some large changes in the model guidance
overnight.  The range of possible outcomes is still large, and
the possibility of a hurricane landfall in the Carolinas still
cannot be ruled out.

3.  Efforts continue to provide the forecast models with as much
data as possible.  The NOAA G-IV jet flew the first in a series of
missions in the storm environment last night, and these missions
will continue today.  The National Weather Service also continues to
launch extra balloon soundings.

4.  Because landfall, if it occurs, is still more than three days
away, it's too early to talk about specific wind, rain, or surge
impacts from Joaquin in the United States.  Regardless of Joaquin's
track, strong onshore winds will create minor to moderate coastal
flooding along the coasts of the mid-Atlantic and northeastern
states through the weekend.

5.  A hurricane watch for a portion of the U.S. coast could be
required as early as tonight.

6.  Many portions of the eastern U.S. are currently experiencing
heavy rains and gusty winds associated with a frontal system. These
heavy rains are likely to continue for the next few days, even if
the center of Joaquin stays offshore.  The resulting inland flood
potential could complicate preparations for Joaquin should it head
toward the coast, and even more substantial inland flooding is
possible if Joaquin later passes near or over these same areas.

FORECAST POSITIONS AND MAX WINDS

INIT  01/0900Z 23.4N  73.7W  105 KT 120 MPH
 12H  01/1800Z 23.1N  74.2W  115 KT 130 MPH
 24H  02/0600Z 23.4N  74.8W  120 KT 140 MPH
 36H  02/1800Z 25.0N  74.8W  120 KT 140 MPH
 48H  03/0600Z 26.8N  74.1W  110 KT 125 MPH
 72H  04/0600Z 32.5N  74.0W   95 KT 110 MPH
 96H  05/0600Z 36.0N  74.5W   80 KT  90 MPH
120H  06/0600Z 39.0N  74.0W   60 KT  70 MPH

$$
Forecaster Brennan
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