#900 Postby cycloneye » Wed Sep 30, 2015 9:58 am
Very long discussion that has tips.
HURRICANE JOAQUIN DISCUSSION NUMBER 11
NWS NATIONAL HURRICANE CENTER MIAMI FL AL112015
1100 AM EDT WED SEP 30 2015
Joaquin has continued to strengthen overnight. Satellite imagery
shows that the convection has become more symmetric, and recent
visible images show what might be an eye trying to form. An Air
Force Reserve Hurricane Hunter aircraft reported 700-mb flight-
level winds of 83 kt and estimated 70 kt surface winds from the
Stepped Frequency Microwave Radiometer, with a central pressure of
971 mb estimated from the aircraft data. Based on these, the
initial intensity is increased to 70 kt.
Joaquin has moved a little south of the previous track with an
initial motion of 230/5. 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.
This is expected to cause the hurricane to turn northward by 72
hours. There is disagreement in the track guidance between the
ECMWF and the other dynamical models. The majority of the guidance
forecasts Joaquin to turn west of north after 48-72 hours, with the
storm moving inland over the mid-Atlantic states and merging with
the trough. On the other hand, the ECMWF forecast the hurricane to
move out to sea between North America and Bermuda. The ECMWF
forecasts Joaquin to move more to the south during the first 24-48
hours than the other models. In addition, it shows the hurricane
interacting with an upper-level low to its northeast that results in
a more eastward motion after 48 hours. The new forecast track,
which is similar to the previous track, leans more toward the
non-ECMWF guidance. However, out of deference to the ECMWF, it
lies to the east of the center of the guidance envelope and the
consensus models. The NOAA G-IV jet is scheduled to fly a synoptic
surveillance mission this afternoon, which, along with special
rawinsonde launches over the eastern U. S., hopefully will reduce
the spread of the guidance.
Joaquin is expected to remain in an environment of moderate
northeasterly vertical shear for the next 24-36 hours. 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 72 hours. Based on this, the intensity forecast calls for
Joaquin to peak as a major hurricane in about 72 hours, and it is
possible it could be stronger than currently forecast. After 72
hours, increasing shear and cold air intrusion should cause
weakening and the start of extratropical transition.
KEY MESSAGES:
1. Confidence in the details of the track forecast late in the
period remains low, since the environmental steering currents are
complex and the model guidance is inconsistent. A wide range of
outcomes is possible, from a direct impact of a major hurricane
along the U.S. east coast to a track of Joaquin out to sea away from
the coast. It is therefore way too soon to talk about specific
wind, rain, or surge impacts from Joaquin in the U.S.
2. Should the threat to the U.S. increase, any further adjustments
of the forecast to the west would likely be accompanied by an
increase in the forecast forward speed, with impacts along the coast
occurring sooner than currently forecast. A hurricane watch could
be required for portions of the U.S. coast as early as Thursday
evening.
3. 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.
FORECAST POSITIONS AND MAX WINDS
INIT 30/1500Z 24.7N 72.6W 70 KT 80 MPH
12H 01/0000Z 24.3N 73.2W 80 KT 90 MPH
24H 01/1200Z 24.1N 74.0W 85 KT 100 MPH
36H 02/0000Z 24.4N 74.4W 90 KT 105 MPH
48H 02/1200Z 25.3N 74.5W 95 KT 110 MPH
72H 03/1200Z 28.5N 73.5W 100 KT 115 MPH
96H 04/1200Z 34.0N 73.0W 90 KT 105 MPH
120H 05/1200Z 38.5N 74.0W 75 KT 85 MPH
$$
Forecaster Beven
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