Irma has become a major hurricane
Posted by Chris in Tampa on 8/31/2017, 4:48 pm
5 day track:
http://www.nhc.noaa.gov/refresh/graphics_at1+shtml/?cone#contents


https://twitter.com/NHC_Atlantic/status/903356914351923200






Hurricane Irma Discussion Number   6
NWS National Hurricane Center Miami FL       AL112017
500 PM AST Thu Aug 31 2017

Irma has become an impressive hurricane with intense eyewall
convection surrounding a small eye.  Satellite estimates continue to
rapidly rise, and the Dvorak classifications from both TAFB & SAB
support an initial wind speed of 100 kt.  This is a remarkable 50-kt
increase from yesterday at this time.

Microwave and satellite data suggest that an eyewall replacement
cycle could be starting.  This isn't surprising given how small the
eye is, and will probably be the first of many eyewall cycles for
this hurricane.  Overall, Irma should be in a low-shear environment
for several days, with the intensity controlled by eyewall cycles
and the moderately warm SSTs along the path.  Thus the forecast
intensity is leveled off for the next 2 days.  After the weekend,
Irma should be moving over much warmer water, with SSTs forecast to
be 29C at the end of the period.  All indications are for Irma to be
strengthening by the end of the forecast period, with the NHC
prediction adjusted slightly upward from the previous one, in line
with the extremely low pressures forecast by the global and regional
hurricane models at that time.

Irma continues moving west-northwestward, now at about 10 kt.
There has been no change to the forecast philosophy, with the
hurricane likely to turn westward and west-southwestward over the
next few days due to a building ridge over the central Atlantic.  At
long range, however, model guidance is not in good agreement on the
strength of the ridge, resulting in some significant north-south
differences in the global models.  I am inclined to stay on the
southwestern side of the model guidance, given the rather consistent
forecasts of the ECMWF and its ensemble.  In addition, the strongest
members of the recent ensembles are on the southern side on the
consensus, giving some confidence in that approach.


FORECAST POSITIONS AND MAX WINDS

INIT  31/2100Z 17.3N  34.8W  100 KT 115 MPH
12H  01/0600Z 17.8N  36.2W  105 KT 120 MPH
24H  01/1800Z 18.2N  38.3W  105 KT 120 MPH
36H  02/0600Z 18.3N  40.7W  105 KT 120 MPH
48H  02/1800Z 17.9N  42.9W  105 KT 120 MPH
72H  03/1800Z 16.8N  47.5W  110 KT 125 MPH
96H  04/1800Z 16.0N  52.0W  115 KT 130 MPH
120H  05/1800Z 16.5N  56.5W  120 KT 140 MPH

$$
Forecaster Blake






Hurricane Irma Advisory Number   6
NWS National Hurricane Center Miami FL       AL112017
500 PM AST Thu Aug 31 2017

...IRMA BECOMES A CATEGORY 3 HURRICANE OVER THE EASTERN ATLANTIC...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...17.3N 34.8W
ABOUT 720 MI...1160 KM W OF THE CABO VERDE ISLANDS
ABOUT 1780 MI...2865 KM E OF THE LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...115 MPH...185 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...967 MB...28.56 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
At 500 PM AST (2100 UTC), the center of Hurricane Irma was located
near latitude 17.3 North, longitude 34.8 West.  Irma is moving
toward the west-northwest near 12 mph (19 km/h).  This motion is
expected to continue today, followed by a westward turn on Saturday,
and a west-southwestward motion by Sunday.

Maximum sustained winds have increased to near 115 mph (185 km/h)
with higher gusts.  Irma is a category 3 hurricane on the
Saffir-Simpson Hurricane Wind Scale.  Fluctuations in strength,
both up and down, are possible, but Irma is expected to remain a
powerful hurricane for several days.

Hurricane-force winds extend outward up to 15 miles (30 km) from the
center and tropical-storm-force winds extend outward up to 80 miles
(130 km).

The estimated minimum central pressure is 967 mb (28.56 inches).


HAZARDS AFFECTING LAND
----------------------
None


NEXT ADVISORY
-------------
Next complete advisory at 1100 PM AST.

$$
Forecaster Blake
433
In this thread:
Irma has become a major hurricane - Chris in Tampa, 8/31/2017, 4:48 pm
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