Hurricane IRMA (Text)


Hurricane Irma Discussion Number   8
NWS National Hurricane Center Miami FL       AL112017
500 AM AST Fri Sep 01 2017

After rapidly strengthening on Thursday, Irma appears to have
leveled off in intensity.  The eye of the hurricane remains
evident in satellite images, but it has occasionally been cloud
filled.  The deep convection in the eyewall has been fairly
symmetric, and the Dvorak CI-numbers from TAFB and SAB have held
steady at 5.5/102 kt.  Based on these data, the initial wind
speed remains 100 kt for this advisory.

Although Irma is in a very low wind shear environment, the hurricane
is moving over only marginally warm SSTs and is in close proximity
to dry air.  The models respond to these conditions by showing
little change in strength or some weakening during the next couple
of days.  Thereafter, Irma is expected to move into a more favorable
thermodynamic environment while remaining in low wind shear
conditions, which should allow the hurricane to intensify.  It
should be noted that major hurricanes like Irma often undergo
eyewall replacements that can cause fluctuations in strength, but
unfortunately these internal dynamics can not be forecast with any
accuracy.  The NHC intensity forecast is identical to the previous
one and lies near the high end of the model guidance.

Irma is moving west-northwestward at 10 kt to the south of a
subtropical high pressure system.  This high is forecast to
strengthen and build westward during the next few days, which
should cause the hurricane to turn to the west in about 24 hours and
then move to the west-southwest over the weekend.  By the end of the
forecast period, Irma is expected to move on the south side of the
high, which should cause the storm to turn back to the west or
west-northwest.  Although the models agree on this overall scenario,
they differ slightly on the strength and orientation of the high and
the intensity of Irma.  These differences have caused a fair amount
of north-south spread.  The NHC intensity forecast lies near the
middle of the guidance envelope through day 4, but leans toward the
southern end at day 5, in favor of the ECMWF and HCCA models.


INIT  01/0900Z 18.2N  36.5W  100 KT 115 MPH
 12H  01/1800Z 18.5N  38.2W  100 KT 115 MPH
 24H  02/0600Z 18.4N  40.5W  100 KT 115 MPH
 36H  02/1800Z 18.2N  42.9W  100 KT 115 MPH
 48H  03/0600Z 17.6N  45.2W  105 KT 120 MPH
 72H  04/0600Z 16.5N  49.3W  110 KT 125 MPH
 96H  05/0600Z 16.5N  53.5W  115 KT 130 MPH
120H  06/0600Z 17.5N  58.0W  120 KT 140 MPH

Forecaster Cangialosi


Standard version of this page

Alternate Formats
About Alternates - E-Mail Advisories - RSS Feeds

Cyclone Forecasts
Latest Advisory - Past Advisories - About Advisories

Marine Forecasts
Latest Products - About Marine Products

Tools & Data
Satellite Imagery - US Weather Radar - Aircraft Recon - Local Data Archive - Forecast Verification - Deadliest/Costliest/Most Intense

Learn About Hurricanes
Storm Names Wind Scale - Prepare - Climatology - NHC Glossary - NHC Acronyms - Frequently Asked Questions - AOML Hurricane-Research Division

About Us
About NHC - Mission/Vision - Other NCEP Centers - NHC Staff - Visitor Information - NHC Library

Contact Us

NOAA/ National Weather Service
National Centers for Environmental Prediction
National Hurricane Center
11691 SW 17th Street
Miami, Florida, 33165-2149 USA
Privacy Policy
About Us
Career Opportunities
Page last modified: Sunday, 31-Dec-2017 12:09:24 UTC