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Hurricane Irma Discussion Number  24
NWS National Hurricane Center Miami FL       AL112017
500 AM AST Tue Sep 05 2017

The cloud pattern on satellite is spectacular with a clear eye
surrounded by a ring of very deep convection. An Air Force plane
was in the eye of the hurricane a few hours ago and measured
surface winds of 126 kt with the SFMR. Since the plane left, the
could pattern has become even more impressive and objective
T-numbers have been oscillating around 7.0 on the Dvorak scale.
Based on the average of these estimates, the initial intensity
is adjusted upward to 130 kt.

The hurricane will be moving through an environment of low vertical
wind shear, a moist mid-level atmosphere, and increasing upper-ocean
heat content, and this is ideal for some additional intensification.
However, given that the SHIPS models do not show any significant
change in the intensity, the NHC forecast keeps Irma a powerful
hurricane through five days.

Recon and satellite fixes indicate that Irma is moving toward the
west or 270 degrees at 12 kt. The hurricane is moving around the
periphery of the Atlantic subtropical ridge, which in fact is quite
strong at this time. This persistent pattern should keep Irma on a
general westward track for the next 24 hours, with a west-northwest
track thereafter. The guidance envelope and many of the ensemble
members of the GFS and the ECMWF models have shifted slightly
westward since the previous run. The NHC forecast also shifted
slightly westward, and it is on top of the multi-model consensus.
The confidence in the forecast beyond 3 days is lower, since the
guidance spreads out more.

Users are reminded to not focus on the exact forecast track,
especially at the longer ranges, since the average NHC track errors
are about 175 and 225 statute miles at days 4 and 5, respectively.

KEY MESSAGES:

1. Irma is expected to affect the northeastern Leeward Islands as a
dangerous major hurricane, accompanied by life-threatening wind,
storm surge, and rainfall impacts.  Hurricane warnings are in effect
for portions of the Leeward Islands.  Preparations should be rushed
to completion, as tropical-storm force winds are expected to first
arrive in the hurricane warning area later today.

2. Irma is also expected to affect the British and U.S. Virgin
Islands and Puerto Rico as a dangerous major hurricane later this
week.  Hurricane warnings have been issued for these areas, and
tropical-storm-force winds could arrive in these areas by early
Wednesday.

3. Irma could directly affect Hispaniola, the Turks and Caicos, the
Bahamas, and Cuba as a dangerous major hurricane later this week.
Residents in these areas should monitor the progress of Irma and
listen to advice given by officials.

4. There is an increasing chance of seeing some impacts from Irma in
the Florida Peninsula and the Florida Keys later this week and this
weekend.  Otherwise, it is still too early to determine what direct
impacts Irma might have on the continental United States.  However,
everyone in hurricane-prone areas should ensure that they have their
hurricane plan in place.


FORECAST POSITIONS AND MAX WINDS

INIT  05/0900Z 16.6N  57.0W  130 KT 150 MPH
 12H  05/1800Z 17.0N  58.9W  130 KT 150 MPH
 24H  06/0600Z 17.7N  61.5W  130 KT 150 MPH
 36H  06/1800Z 18.6N  64.2W  130 KT 150 MPH
 48H  07/0600Z 19.6N  67.0W  125 KT 145 MPH
 72H  08/0600Z 21.2N  72.5W  120 KT 140 MPH
 96H  09/0600Z 22.4N  77.2W  115 KT 130 MPH
120H  10/0600Z 24.0N  81.0W  115 KT 130 MPH

$$
Forecaster Avila

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