#1097 Postby cycloneye » Wed Sep 30, 2015 3:58 pm
Much longer discussion than the 11 AM.
HURRICANE JOAQUIN DISCUSSION NUMBER 12
NWS NATIONAL HURRICANE CENTER MIAMI FL AL112015
500 PM EDT WED SEP 30 2015
There has been little change in the organization of Joaquin during
the past several hours. While the hurricane continues to produce
cloud tops colder than -80C in the eyewall, the eye has not become
better defined since the last advisory. Satellite intensity
estimates are 77 kt from both TAFB and SAB, so the advisory
intensity is now 75 kt.
The initial motion is 225/7. The shortwave ridge causing this
motion is expected to weaken during the next 24-48 hours as a strong
deep-layer trough develops over the southeastern United States.
Thus, a generally southwestward motion is expected for the next 36
hours or so, followed by a turn toward the north as the trough
becomes the dominant steering mechanism. There is an increased
disagreement between the GFS, UKMET, Canadian, and NAVGEM models
versus the ECMWF since the last advisory. The ECMWF has continued
its forecast of showing a northeastward motion after 72 hours,
taking Joaquin just west of Bermuda and out to sea. The other
models have all shifted their forecasts to the left and now
call for landfall in the Carolinas and the mid-Atlantic states,
followed by merger with the baroclinic trough. Given the shift in
the non-ECMWF models, a major westward adjustment has been made to
the forecast track at 96 and 120 hours, bringing the center of
Joaquin near or over portions of the mid-Atlantic states. Due to
the use of the ECMWF in the consensus models, the new track lies
near the various consensus models. However, it lies well to the
east of the GFS and the other similar models. The NOAA G-IV jet is
currently flying a synoptic surveillance mission, which, along with
special rawinsonde launches, hopefully will reduce the spread of the
guidance.
There is little change to the intensity forecast philosophy since
the last advisory. Joaquin is expected to remain in an environment
of moderate northeasterly vertical shear for the next 24-36 hours,
possibly including strong winds seen at 400 mb in recent dropsondes
from the G-IV aircraft. However, since it has been steadily
strengthening in such an environment, there is no obvious reason to
think it will stop doing so. After 36 hours, the hurricane is
likely to move into an area of divergent southerly upper-level winds
associated with the eastern U. S. trough. While there is
uncertainty as to how much shear should occur, it is expected that
additional intensification could occur through at least 48 hours.
Based on this, the intensity forecast calls for Joaquin to peak as a
major hurricane in 48-72 hours, and it is possible it could be
stronger than currently forecast. After 72 hours, increasing shear,
cold air intrusion, and land interaction should cause weakening and
the start of extratropical transition.
KEY MESSAGES:
1. Preparations to protect life and property within the warning
areas in the Bahamas should be rushed to completion.
2. A significant adjustment to the forecast has been made this
afternoon, and this shows an increased threat to the mid-Atlantic
states and the Carolinas. However, confidence in the details of the
forecast after 72 hours remains low, since we have one normally
excellent model that keeps Joaquin far away from the United States
east coast. The range of possible outcomes is still large, and
includes the possibility of a major hurricane landfall in the
Carolinas.
3. Every effort is being made to provide the forecast models with
as much data as possible. The NOAA G-IV jet has begun a series of
missions in the storm environment, and the National Weather Service
is launching extra balloon soundings.
4. Because landfall, if it occurs, is still more than three days
away, it is too early to talk about specific wind, rain, or surge
impacts from Joaquin in the United States. Even if Joaquin stays
well out to sea, 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 Thursday evening.
6. Many areas of the eastern U.S. are currently experiencing heavy
rains and gusty winds associated with a frontal system. This
inclement weather is expected to continue over the next few days,
which could complicate preparations for Joaquin should it head
toward the coast, and greatly exacerbate the impacts from the
hurricane. Heavy rains are likely to continue over these areas
even if the center of Joaquin stays out to sea.
FORECAST POSITIONS AND MAX WINDS
INIT 30/2100Z 24.3N 73.1W 75 KT 85 MPH
12H 01/0600Z 24.0N 73.8W 85 KT 100 MPH
24H 01/1800Z 23.9N 74.5W 90 KT 105 MPH
36H 02/0600Z 24.5N 75.0W 95 KT 110 MPH
48H 02/1800Z 25.8N 75.0W 100 KT 115 MPH
72H 03/1800Z 30.5N 74.5W 100 KT 115 MPH
96H 04/1800Z 36.0N 75.5W 85 KT 100 MPH
120H 05/1800Z 38.5N 76.5W 55 KT 65 MPH
$$
Forecaster Beven
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