Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
200 AM EDT Fri Sep 1 2017

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Hurricane
Irma, located over the eastern Atlantic Ocean. The Weather
Prediction Center is issuing advisories on Tropical Depression
Harvey, located over northern Mississippi.

1. A tropical wave located over the far eastern Atlantic Ocean just off
the west coast of Africa is producing disorganized showers and
thunderstorms. Environmental conditions are expected to be
conducive for development, and this system could become a tropical
depression early next week while it moves westward at 15 mph over
the tropical Atlantic.
* Formation chance through 48 hours…low…near 0 percent.
* Formation chance through 5 days…medium…50 percent.

Forecaster Cangialosi

IRMA HOLDING STEADY WITH 115-MPH WINDS

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.

FORECAST POSITIONS AND MAX WINDS

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

CENTER OF LIDIA MOVING ONSHORE INTO BAJA CALIFORNIA SUR… …HEAVY RAINS CONTINUE OVER SOUTHERN BAJA CALIFORNIA SUR