Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Sun Sep 10 2017

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

The National Hurricane Center is issuing advisories on Hurricane
Irma, located near the Florida Keys. The Weather Prediction Center
is issuing advisories on Hurricane Jose, located a couple hundred
miles north-northwest of the northern Leeward Islands.

1. Showers and thunderstorms associated with a tropical wave
located a few hundred miles south-southwest of the Cabo Verde
Islands continue to show some signs of organization. Environmental
conditions are expected to be conducive for some development, and a
tropical depression could form during the next few days while the
system moves generally northwestward over the eastern Atlantic
Ocean.
* Formation chance through 48 hours…low…30 percent.
* Formation chance through 5 days…medium…60 percent.

Forecaster Landsea

 

CENTER OF IRMA ABOUT TO MAKE LANDFALL IN THE LOWER FLORIDA KEYS

Hurricane Irma Discussion Number 45
NWS National Hurricane Center Miami FL AL112017
500 AM EDT Sun Sep 10 2017

An Air Force Reserve Hurricane Hunter aircraft reported 700-mb
flight-level winds of 128 kt in the northeastern eyewall, along with
surface wind estimates of 110-115 kt from the Stepped Frequency
Microwave Radiometer. In addition, the aircraft data shows that the
central pressure has fallen to 928 mb. Based on these data, the
initial intensity has been increased to 115 kt, again making Irma a
Category 4 hurricane.

Irma has made its long-awaited turn, with the initial motion now
325/7. For the next 36-48 h, the cyclone will be steered generally
north-northwestward with an increase in forward speed between a low-
to mid-level ridge over the western Atlantic and a developing mid-
to upper-level low over the Gulf Coast states and the northern Gulf
of Mexico. After that, the system should turn northwestward and
then move somewhat erratically near the end of its life as it merges
with the low. The tightly-clustered track guidance has changed
little since the last advisory, and the new NHC forecast is very
close to the previous one. The eye should move across the Lower
Florida Keys in the next few hours. After that, the hurricane’s
track almost parallel to the west coast of Florida makes it very
difficult to pinpoint exactly where Irma will cross the Florida Gulf
coast.

Given current trends, some additional strengthening could occur
during the next several hours. However, vertical wind shear is
increasing over Irma, and the shear is expected to become strong
within 24 h. This, combined with land interaction, should cause at
least a steady weakening from 12-36 h. The new intensity forecast
is slightly lower than that of the previous advisory at those
times, but it still calls for Irma to be a major hurricane at its
closest approach to the Tampa Bay area. A faster weakening is
likely after Irma moves across the Florida Panhandle and starts to
merge with the aforementioned upper-level low, and the new forecast
follows the trend of the previous one in calling for the system to
decay to a remnant low by 72 h and to dissipate completely by 120 h.

KEY MESSAGES:

1. Irma is expected bring life-threatening wind and storm surge to
the Florida Keys and southwestern Florida as an extremely dangerous
major hurricane today, and these conditions will spread into central
and northwestern Florida tonight and Monday. Preparations in the
Florida Keys and southwest Florida should be complete since
hurricane-force winds are spreading into that area.

2. There is an imminent danger of life-threatening storm surge
flooding along much of the Florida west coast, including the Florida
Keys, where a Storm Surge Warning is in effect. The threat of
catastrophic storm surge flooding is highest along the southwest
coast of Florida, where 10 to 15 feet of inundation above ground
level is expected. This is a life-threatening situation.

3. Irma will bring life-threatening wind impacts to much of Florida
regardless of the exact track of the center. Wind hazards from Irma
are also expected to spread northward through much of Georgia
and portions of South Carolina and Alabama.

4. Irma is expected to produce very heavy rain and inland flooding.
Total rain accumulations of 15 to 20 inches with isolated amounts of
25 inches are expected over the Florida Keys through Sunday evening.
Through Monday, Irma is expected to produce rainfall amounts of 8 to
15 inches with isolated amounts of 20 inches across the Florida
peninsula and southeast Georgia, while across the rest of Georgia,
eastern Florida Panhandle, southern and western South Carolina, and
western North Carolina, a total of 3 to 6 inches with isolated
amounts of 10 inches are expected. Significant river flooding is
possible in these areas. Through Tuesday, Irma will also bring
periods of heavy rain into the Tennessee Valley, where an average of
2 to 5 inches with isolated higher amounts is forecast across
eastern Alabama and southern Tennessee. This includes some
mountainous areas which are more prone to flash flooding. Residents
throughout the southeast states should remain aware of the flood
threat and stay tuned to forecasts and warnings.

FORECAST POSITIONS AND MAX WINDS

INIT 10/0900Z 24.1N 81.5W 115 KT 130 MPH
12H 10/1800Z 25.4N 82.0W 115 KT 130 MPH
24H 11/0600Z 27.8N 82.8W 100 KT 115 MPH
36H 11/1800Z 30.5N 84.1W 75 KT 85 MPH…INLAND
48H 12/0600Z 32.7N 85.8W 40 KT 45 MPH…INLAND
72H 13/0600Z 35.5N 89.0W 25 KT 30 MPH…POST-TROP/INLAND
96H 14/0600Z 37.5N 88.0W 20 KT 25 MPH…POST-TROP/INLAND
120H 15/0600Z…DISSIPATED

$$
Forecaster Beven

 

JOSE PASSING WELL NORTH OF PUERTO RICO THIS MORNING… …NOAA BUOY REPORTS WIND GUST TO 110 MPH

Hurricane Jose Discussion Number 20
NWS National Hurricane Center Miami FL AL122017
Issued by the NWS Weather Prediction Center College Park MD
500 AM AST Sun Sep 10 2017

Jose remains a category four hurricane on the Saffir-Simpson
Hurricane Wind Scale, with a 15 n mi wide eye continuing to be
surrounded a solid ring of deep convection. Little significant
change in the overall satellite appearance has been observed since a
Hurricane Hunter plane sampled the cyclone earlier in the night, and
the initial intensity remains unchanged at 115 kt.

The initial motion is 310/14 kt, with Jose’s track through the first
24 hours being driven by a mid-level ridge located to the
north-northeast of the cyclone. After this time, the steering
pattern is expected to become rather dynamic, leading to a
5-day forecast that shows Jose making a small anticyclonic loop
over the open waters of the western Atlantic. This occurs as the
ridge shifts to the east of Jose from 36 to 48 hours, leading to a
reduction in forward speed, and a gradual turn toward the north. A
turn toward the east and southeast is expected on days 3 and 4, with
an even slower forward motion, as the ridge weakens and moves south
of the system. Late in the forecast period, the ridge is expected to
build to the northwest and then north of Jose, leading to a gradual
acceleration toward the west, and a reduction in the shear. With
such a complex steering pattern expected, it comes as no surprise
that the track guidance diverges significantly in the latter
forecast periods. The updated forecast is close to the previous one,
lies close to the FSSE, and is in between the GFS and ECMWF, which
are more than 250 miles apart on day 5.

The shear over Jose is currently analyzed to be near 10 kt, but
north to northeasterly shear is forecast to increase in the short
term and remain relatively strong through 48 hours due to Jose
moving closer to a building ridge to its northwest. This will
lead to a weakening trend, despite the system remaining over SSTs
near 29 Celsius. The official intensity forecast is nudged down ever
so slightly from the previous one through day 3, but remains higher
than the SHIPS model, due to the ECMWF and GFS models maintaining a
more intense system. The intensity prediction on days 4 and 5
remains unchanged due to forecast environmental uncertainties at
that time.

FORECAST POSITIONS AND MAX WINDS

INIT 10/0900Z 20.8N 64.5W 115 KT 130 MPH
12H 10/1800Z 22.2N 66.1W 110 KT 125 MPH
24H 11/0600Z 24.2N 67.9W 105 KT 120 MPH
36H 11/1800Z 25.6N 69.0W 100 KT 115 MPH
48H 12/0600Z 26.5N 68.8W 95 KT 110 MPH
72H 13/0600Z 26.3N 67.0W 90 KT 105 MPH
96H 14/0600Z 25.0N 66.5W 90 KT 105 MPH
120H 15/0600Z 24.5N 70.0W 90 KT 105 MPH

$$
Forecaster Birchard/Blake