Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
200 AM EDT Mon Sep 11 2017

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

The National Hurricane Center is issuing advisories on Hurricane
Irma, located inland over west-central Florida. The Weather
Prediction Center is issuing advisories on Hurricane Jose,
located a few hundred miles north of the Dominican Republic.

1. A tropical wave located several hundred miles west-southwest of the
Cabo Verde Islands continues to produce disorganized showers and
thunderstorms. Some development of this system is possible during
the next couple of days before upper-level winds become unfavorable
for tropical cyclone formation. This system is expected to move
west-northwestward for the next two days and then turn northward
over the central Atlantic.
* Formation chance through 48 hours…low…30 percent.
* Formation chance through 5 days…medium…40 percent.

Forecaster Cangialosi/Ramos

 

IRMA CONTINUES TO WEAKEN AS THE CENTER MOVES ALONG THE NORTHWESTERN COAST OF THE FLORIDA PENINSULA

Hurricane Irma Discussion Number 49
NWS National Hurricane Center Miami FL AL112017
500 AM EDT Mon Sep 11 2017

Irma is continuing to weaken as it moves across the western Florida
peninsula, with the eye dissipating and weakening banding near the
center. There are no recent observations of hurricane-force winds
near the center, but based on the premise that such winds still
exist over the Gulf of Mexico west of the center the initial
intensity is reduced to 65 kt. It should be noted that near-
hurricane force winds are occurring in a band well northeast of the
center with sustained winds of 60 kt reported in the Jacksonville
area. The cyclone should continue to weaken as it moves through
the southeastern United States, becoming a tropical storm later
today, a tropical depression by 36 h, and a remnant low by 48 h. The
large-scale models forecast Irma to dissipate completely by 72 h,
so the 72 h point has been removed from the forecast.

The initial motion is 340/16. The cyclone is expected to move
around the eastern side of a mid-level disturbance currently located
along the U.S. Gulf Coast, which should cause a north-northwestward
to northwestward motion until dissipation. The forecast track
takes the center across the eastern Florida Panhandle, southwestern
Georgia, eastern and northern Alabama, and eventually into western
Tennessee.

KEY MESSAGES:

1. There is the danger of life-threatening storm surge flooding
along portions of the coasts of Florida, Georgia and South Carolina,
where a Storm Surge Warning remains in effect.

2. Irma will continue to bring life-threatening wind impacts to much
of central and north Florida, with hurricane-force winds near the
center. Also, Irma is a large hurricane, and hurricane-force wind
gusts and sustained tropical-storm force winds extend far from the
center. Wind hazards from Irma will continue to spread northward
through Georgia and into portions of Alabama, Tennessee, South
Carolina, and North Carolina.

3. Irma continues to produce very heavy rain and inland flooding
across much of the northern peninsula and eastern panhandle of
Florida and southern Georgia, which is quickly spreading to the rest
of the southeast United States. Intense rainfall rates of 2 inches
or more per hour is leading to flash flooding and rapid rises on
creeks, streams, and rivers. Significant river flooding is likely
over the next five days in the Florida peninsula and southern
Georgia, where average rainfall totals of 8 to 15 inches are
expected. Significant river flooding is possible beginning Monday
and Tuesday in much of central Georgia and southern South Carolina
where average rainfall of 3 to 6 inches and isolated 10 inch amounts
are expected. Portions of these states within the southern
Appalachians will be especially vulnerable to flash flooding.
Farther north and west, Irma is expected to produce average amounts
of 2 to 4 inches in parts of Mississippi, Alabama, and Tennessee,
northern South Carolina and western North Carolina, where isolated
higher amounts and local flooding may occur.

FORECAST POSITIONS AND MAX WINDS

INIT 11/0900Z 28.9N 82.6W 65 KT 75 MPH…INLAND
12H 11/1800Z 30.8N 83.7W 55 KT 65 MPH…INLAND
24H 12/0600Z 33.0N 85.7W 35 KT 40 MPH…INLAND
36H 12/1800Z 34.5N 87.8W 25 KT 30 MPH…INLAND
48H 13/0600Z 35.5N 89.0W 20 KT 25 MPH…POST-TROP/INLAND
72H 14/0600Z…DISSIPATED

$$
Forecaster Beven

 

WEAKENING JOSE EXPECTED TO LINGER OVER THE WESTERN ATLANTIC FOR SEVERAL DAYS

Hurricane Hurricane Jose Discussion Number 24
NWS National Hurricane Center Miami FL AL122017
Issued by the NWS Weather Prediction Center College Park MD
500 AM AST Mon Sep 11 2017

Although Jose’s satellite appearance is somewhat degraded due to the
effects of northeasterly shear estimated to be near 25 kt, it has
been able to maintain persistent deep convection over the center. A
well-timed 0456Z GPM overpass helped to confirm that the center was
on the north side of the cold cloud tops while also highlighting
that an eye feature persists despite being obscured in conventional
imagery. Subjective and objective satellite-based intensity
estimates indicate that Jose continues on a weakening trend, and
this supports lowering the initial intensity to 90 kt for this advisory.

The initial motion is estimated to be 335/09 kt as Jose continues
to track around the western side of a mid-level ridge. As this ridge
shifts to the southeast and south of Jose over the next 12 to 24
hours, its forward motion will slow, and the system will begin to
move toward the northeast. On days 2 and 3 a ridge will begin to
strengthen to the northwest of Jose, driving the system toward the
southeast. By day 4 the ridge will move to a position north of
Jose, which will gradually accelerate Jose toward the west-northwest
through day 5. The expectation is that Jose will complete a small
clockwise loop over the open waters of the western Atlantic the next
couple of days. Despite the complex forecast track, this general
solution is shared by all the reliable model guidance. The official
track forecast is shifted slightly north from the previous one due
to a northward shift in the ECMWF guidance, and is close to the GFEX
consensus model.

The northeasterly shear currently over Jose will shift to the
northwest and will ease a little, but remain strong enough to keep
Jose on a weakening trend through day 3. Although SSTs in the area
are warm enough to support an intense hurricane, a slow-moving and
looping Jose will likely move over its own cold wake around day 3,
as seen in HWRF guidance. On days 4 and 5, Jose will move toward
warmer water while the shear relaxes, and there is a potential for
reintensification. The latest intensity forecast is very close to
the IVCN consensus, but it is more aggressive in weakening Jose than
the SHIPS model, which is not accounting for interaction with the
cold wake.

A 1222Z ASCAT pass sampled Jose nearly perfectly, and the 34/50 kt
wind radii were adjusted based on this data.

FORECAST POSITIONS AND MAX WINDS

INIT 11/0900Z 24.4N 68.6W 90 KT 105 MPH
12H 11/1800Z 25.8N 69.3W 80 KT 90 MPH
24H 12/0600Z 26.8N 69.0W 75 KT 85 MPH
36H 12/1800Z 27.0N 67.6W 70 KT 80 MPH
48H 13/0600Z 26.3N 66.5W 70 KT 80 MPH
72H 14/0600Z 24.5N 65.5W 65 KT 75 MPH
96H 15/0600Z 25.0N 69.0W 70 KT 80 MPH
120H 16/0600Z 26.5N 73.0W 80 KT 90 MPH

$$
Forecaster Birchard