[Ray76]

000
WTNT41 KNHC 050237
TCDAT1

Hurricane Irma Discussion Number  23
NWS National Hurricane Center Miami FL       AL112017
1100 PM AST Mon Sep 04 2017

Irma's satellite presentation remains quite impressive with a
well-defined eye and a symmetrical CDO containing very cold cloud
tops. Flight-level and SFMR-observed surface winds from NOAA and
Air Force Hurricane Hunter aircraft indicate that the current
intensity is about 120 kt. Since the hurricane will be moving
through an environment of low vertical wind shear, a moist mid-level
atmosphere, and increasing upper-ocean heat content, additional
intensification is likely. The only expected impediment to
strengthening should be eyewall replacement cycles, which are
difficult to predict. The official intensity forecast is very
close to the latest model consensus, ICON. Although the consensus
of the guidance shows slight weakening in the 96- to 120-hour time
frame, Irma is forecast to remain a powerful hurricane throughout
the 5-day forecast period.

Center fixes from the aircraft indicate a westward motion of about
270/11 kt. Irma should turn toward the west-northwest tomorrow
while it is steered by the flow to the south of a mid-level ridge.
A broad trough is forecast to amplify over the eastern U.S. in
72 hours and then lift northeastward leaving a weakness in the ridge
to north of the hurricane. This should cause a slowing of the
forward speed near the end of the forecast period. The official
track forecast is similar to the previous one and is close to the
model consensus.

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 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 by late Tuesday.

2. Irma is also expected 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 05/0300Z 16.7N 55.6W 120 KT 140 MPH
12H 05/1200Z 16.9N 57.4W 125 KT 145 MPH
24H 06/0000Z 17.5N 60.0W 130 KT 150 MPH
36H 06/1200Z 18.3N 62.7W 130 KT 150 MPH
48H 07/0000Z 19.3N 65.5W 125 KT 145 MPH
72H 08/0000Z 21.2N 71.0W 120 KT 140 MPH
96H 09/0000Z 22.5N 76.0W 115 KT 130 MPH
120H 10/0000Z 24.0N 80.0W 115 KT 130 MPH

$$
Forecaster Pasch

http://www.nhc.noaa.gov/text/refresh/MIATCDAT1+shtml/050237.shtml

[Ray76]

excerpt

000
AXNT20 KNHC 051105
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
705 AM EDT Tue Sep 5 2017

 

The center of Hurricane Irma at 05/1200 UTC is near 16.6N 56.4W, or about 280 nm to the E of the Leeward Islands. Irma is moving W, or about 270 degrees, 12 knots. The estimated minimum central pressure is 937 mb. The maximum sustained wind speeds are 130 kt with gusts to 160 kt. Convective precipitation: Numerous strong is within 120 nm radius of the center. Isolated moderate to locally strong from 12N to 20N between 44W and 53W, and from 10N to 12N between 51W and 55W. Warnings and watches have been issued for the Leeward Islands, Virgin Islands and Puerto Rico. Some strengthening is forecast during the next 48 hours. (emphasis added)

http://www.nhc.noaa.gov/text/refresh/MIATWDAT+shtml/051105_MIATWDAT.shtml?

---

             Saffir-Simpson Hurricane Wind Scale

Category    Sustained Winds      Types of Damage Due to Hurricane Winds
--------    ---------------      --------------------------------------
1              74-95 mph         Very dangerous winds will produce some 
               64-82 kt          damage: Well-constructed frame homes could 
                                 have damage to roof, shingles, vinyl siding 
                                 and gutters. Large branches of trees will 
                                 snap and shallowly rooted trees may be 
                                 toppled. Extensive damage to power lines 
                                 and poles likely will result in power 
                                 outages that could last a few to several 
                                 days.
               
2             96-110 mph         Extremely dangerous winds will cause 
              83-95 kt           extensive damage: Well-constructed frame 
                                 homes could sustain major roof and siding 
                                 damage. Many shallowly rooted trees will 
                                 be snapped or uprooted and block numerous 
                                 roads. Near-total power loss is expected 
                                 with outages that could last from several 
                                 days to weeks. 

3            111-129 mph         Devastating damage will occur: Well-built 
(major)       96-112 kt          framed homes may incur major damage or 
                                 removal of roof decking and gable ends. 
                                 Many trees will be snapped or uprooted, 
                                 blocking numerous roads. Electricity and 
                                 water will be unavailable for several days 
                                 to weeks after the storm passes. 

4            130-156 mph         Catastrophic damage will occur: Well-built 
(major)      113-136 kt          framed homes can sustain severe damage with 
                                 loss of most of the roof structure and/or 
                                 some exterior walls. Most trees will be 
                                 snapped or uprooted and power poles downed. 
                                 Fallen trees and power poles will isolate 
                                 residential areas. Power outages will last 
                                 weeks to possibly months. Most of the area 
                                 will be uninhabitable for weeks or months.

5            157 mph or higher   Catastrophic damage will occur: A high 
(major)      137 kt or higher    percentage of framed homes will be destroyed, 
                                 with total roof failure and wall collapse. 
                                 Fallen trees and power poles will isolate 
                                 residential areas. Power outages will last 
                                 for weeks to possibly months. Most of the 
                                 area will be uninhabitable for weeks or 
                                 months.

http://www.nhc.noaa.gov/aboutsshws.php

Sustained wind means one minute duration