FURTHER UPDATED: 6 Sep Weather in Cayman & Tropical Report, 3 H-canes

Sep 6 Wed 2017

Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Wed Sep 6 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 northern Leeward Islands, on Tropical Storm
Jose, located over the central Atlantic Ocean, and on Tropical Storm
Katia, located over the southwestern Gulf of Mexico.

Tropical cyclone formation is not expected during the next 5 days.

Public Advisories on Katia are issued under WMO header
WTNT33 KNHC and under AWIPS header MIATCPAT3.
Forecast/Advisories on Katia are issued under WMO header
WTNT23 KNHC and under AWIPS header MIATCMAT3.

$$
Forecaster Avila

700 PM AST POSITION UPDATE… …CORE OF IRMA PASSING JUST NORTH OF PUERTO RICO

Hurricane Irma Discussion Number 31
NWS National Hurricane Center Miami FL AL112017
500 PM AST Wed Sep 06 2017

The eye of Irma passed over the northernmost Virgin Islands earlier
this afternoon and it is now located just to their northwest. The
satellite and radar presentation of the hurricane remains extremely
impressive. An Air Force Reserve reconnaissance aircraft reported
peak SFMR winds of 156 kt and flight-level winds of 164 kt during
its mission this afternoon. Although there have been no SFMR or
flight-level winds as high as what was observed yesterday, the
initial intensity remains 160 kt, due to the potential of
undersampling. Dropsonde observations in the eye indicated that the
pressure rose a few millibars this morning, but the most recent
aircraft report shows that the pressure has fallen to 914 mb.

The hurricane remains on a west-northwestward motion at about 14
kt. A high pressure ridge over the western Atlantic is forecast to
keep Irma on a west-northwestward course over the next 48 to 72
hours. The track guidance is still in good agreement during that
period, and little change to the NHC forecast was required. By the
weekend, a shortwave trough diving southward over the east-central
United States is expected to cause Irma to turn northwestward and
northward. The 12Z guidance has generally shifted slightly
westward, closer to the previous NHC forecast. As a result, little
overall change was made to the 4-5 day track forecast. The NHC
track is once again close to the HFIP corrected consensus model.
This is also near the 12Z GEFS ensemble mean, but a little east of
the latest ECMWF ensemble mean. Users are reminded that the average
NHC track errors at days 4 and 5 are about 175 and 225 miles,
respectively.

Low vertical wind shear and warm waters along the forecast track of
Irma should allow it to remain a very powerful hurricane during the
next several days, and the intensity forecast is again near the
upper-end of the guidance and is the same as the previous advisory
through 96 hours. Increasingly southwesterly shear and potential
land interaction late in the period is expected to cause some
decrease in Irma’s strength by day 5.

Efforts to provide the forecast models with as much data as possible
continue, with 6-hourly NWS balloon launches across much of the
continental United States, and the NOAA G-IV aircraft currently
sampling the environment around the storm.

KEY MESSAGES:

1. Irma is a potentially catastrophic category 5 hurricane and will
bring life-threatening wind, storm surge, and rainfall hazards to
Puerto Rico tonight, the northern coast of Hispaniola Thursday, and
the Turks and Caicos and southeastern and central Bahamas Thursday
and Friday.

2. Hurricane watches are in effect for the northwestern Bahamas and
much of Cuba. Irma is likely to bring dangerous wind, storm surge,
and rainfall to portions of these areas on Friday and Saturday.

3. The threat of direct hurricane impacts in Florida over the
weekend and early next week has increased. Hurricane watches could
be issued for portions of the Florida Keys and the Florida peninsula
on Thursday.

FORECAST POSITIONS AND MAX WINDS

INIT 06/2100Z 18.8N 65.4W 160 KT 185 MPH
12H 07/0600Z 19.6N 67.6W 155 KT 180 MPH
24H 07/1800Z 20.7N 70.4W 150 KT 175 MPH
36H 08/0600Z 21.5N 73.1W 145 KT 165 MPH
48H 08/1800Z 22.2N 75.6W 140 KT 160 MPH
72H 09/1800Z 23.2N 79.0W 135 KT 155 MPH
96H 10/1800Z 26.0N 80.2W 125 KT 145 MPH
120H 11/1800Z 31.0N 81.0W 105 KT 120 MPH

$$
Forecaster Brown

QUICKLY STRENGTHENING JOSE BECOMES A HURRICANE

Hurricane Jose Discussion Number 6
NWS National Hurricane Center Miami FL AL122017
500 PM AST Wed Sep 06 2017

Jose has continued to become better organized. Banding convection
has become very symmetric around the center, and the upper-level
outflow has become well established in all quadrants, despite the
presence of Hurricane Irma to the west. An eye-like dimple has
occasionally been observed in visible imagery during the afternoon.
The initial intensity is now 65 kt, based on the latest Dvorak
intensity estimate from TAFB. There is no reason to believe that
the recent intensification trend will end soon. In fact, the SHIPS
Rapid Intensification Index gives a 48 percent chance of
intensification of 30 kt (or more) in the next 24 h. My forecast is
just shy of that, and is close to the intensification rate shown by
the HWRF for the next 36 h. After about 48-72 h, the vertical wind
shear is forecast to increase, and all of the models forecast
weakening. Overall, the NHC forecast is a little above the model
consensus for the first 72 h, but close to IVCN by the end of the
forecast.

A pair of late-arriving ASCAT passes and recent visible imagery
indicate that Jose is a little farther north than previously
estimated. The initial motion estimate is 285/14 kt. Due to the
northward shift of the initial position, the forecast has been
adjusted in that direction for the first 48 h. However, the
reasoning behind the forecast has not changed, and Jose should
continue on a fairly steady west-northwest track, steered primarily
by the subtropical ridge. After that time, a mid-level trough should
cause the ridge to retreat eastward, allowing Jose to gain more
latitude. The global models, especially the ECMWF, are suggesting
that this turn may occur a little later than previously expected,
and have shifted westward a little bit. The new NHC forecast at 96
and 120 h is very close to a blend of the GFS and ECMWF models, and
is about a degree west of the previous forecast.

FORECAST POSITIONS AND MAX WINDS

INIT 06/2100Z 13.9N 45.8W 65 KT 75 MPH
12H 07/0600Z 14.5N 48.0W 75 KT 85 MPH
24H 07/1800Z 15.1N 51.1W 90 KT 105 MPH
36H 08/0600Z 15.8N 54.0W 95 KT 110 MPH
48H 08/1800Z 16.4N 56.4W 100 KT 115 MPH
72H 09/1800Z 18.5N 60.2W 100 KT 115 MPH
96H 10/1800Z 21.5N 63.7W 85 KT 100 MPH
120H 11/1800Z 25.0N 67.5W 70 KT 80 MPH

$$
Forecaster Zelinsky

HURRICANE KATIA FORMS IN THE SOUTHWESTERN GULF OF MEXICO… …A HURRICANE WATCH IS IN EFFECT FOR THE COAST OF THE STATE OF VERACRUZ

Hurricane Katia Discussion Number 5
NWS National Hurricane Center Miami FL AL132017
400 PM CDT Wed Sep 06 2017

An Air Force reconnaissance plane just investigated Katia and found
a much better organized tropical cyclone with a partial eyewall. It
also measured a flight-level wind of 71 kt and 66 kt with the SFMR.
Based on these data and the improved satellite presentation, Katia
is upgraded to a hurricane with 65 kt winds.

The upper-level wind pattern is becoming more favorable, and that
can be observed by the expansion of the outflow. All models continue
to favor intensification, and in fact, the SHIPS RI index gives a
63 percent chance of a 30-kt wind increase in 24 hours. The NHC
forecast calls for strengthening but at this time is not as high as
some of the guidance.

Katia is embedded within very weak steering currents, and it is now
moving slowly toward the southeast at about 3 kt. The hurricane is
forecast to meander in the southwestern Gulf of Mexico for the next
day or two. After that time the global models develop a ridge over
the northern Gulf of Mexico and this flow pattern will steer Katia
southwestward toward the state of Veracruz. The NHC forecast is
basically on top of the multi-model consensus and follows the trend
of the HFIP corrected consensus HCCA.

Given the upward intensity trend and the forecast track toward
the coast, the government of Mexico has issued a hurricane watch
for a portion of the coast of the state of Veracruz. Katia is also
forecast to bring torrential rains primarily to the state of
Veracruz during the next few days.

FORECAST POSITIONS AND MAX WINDS

INIT 06/2100Z 21.7N 95.1W 65 KT 75 MPH
12H 07/0600Z 21.5N 94.7W 70 KT 80 MPH
24H 07/1800Z 21.3N 94.7W 75 KT 85 MPH
36H 08/0600Z 21.1N 95.0W 80 KT 90 MPH
48H 08/1800Z 20.9N 95.9W 80 KT 90 MPH
72H 09/1800Z 19.5N 98.0W 25 KT 30 MPH…POST-TROP/INLAND
96H 10/1800Z…DISSIPATED

$$
Forecaster Avila

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
500 AM PDT Wed Sep 6 2017

For the eastern North Pacific…east of 140 degrees west longitude:

Tropical cyclone formation is not expected during the next 5 days.

$$
Forecaster Avila
NNNN

Weather In Cayman

Synopsis

Isolated showers and thunder along with light winds and seas will continue across the Cayman area for the next 24 hours as a tropical wave moves over the W Caribbean and interacts with an upper level low. Radar images show scattered showers around the Cayman area which continue to move towards the west. The National Hurricane Center in Miami Florida is issuing advisories on Hurricane Irma, tropical storms Jose and Katia. At 4 am Hurricane Irma, a category 5 hurricane was located near 17.9 N and 62.6 W or about 35 miles east-southeast of St. Martin. Irma is moving towards the west-northwest with maximum sustained winds of 185 mph. Further information can be found on Hurricane Irma as well as Tropical Storms Jose and Katia, which are out of our watch area, at www.nhc.noaa.gov.

Sunshine just makes the day a little better, but it can also cause sunburns. Check the UV Report below to be prepared

Humidity: 61% (DOWN from yesterday)

UV: 10.9 VERY HIGH (DOWN from yesterday)

Temperature: Today’s current temperature – See Weather Forecast Top Right of Website. Yesterday: H 92.0°F L 76.59°F

Wind direction TODAY: SE 5-10 mph GC

Wind direction TONIGHT: Light & variable GC

Barometer: 1014:00 mb Steady Rain: Last month: 4.29 in Last 24 hrs 0.00 This month: 1.64 in

16 Rain days in Aug 3 Rain day in Sep 1 day since rain

2016 Season Total: 20.23 in 2017 Season Total: 25.08 in

*NOTE: Official Government record of rainfall on Grand Cayman (Owen Roberts International Airport) 2016: 27.98 inches or 28.22 inches below the 30 year average rainfall of 56.20 inches. All other readings are from SOUTH SOUND.