UPDATE: 7 Sep Weather in Cayman & Tropical Report, 3 H-canes

September 7, 2017

Sep 7 Thu 2017

Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Thu Sep 7 2017

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

The National Hurricane Center is issuing advisories on Hurricane
Irma, located north of the Dominican Republic, on Hurricane Jose,
located over the central Atlantic Ocean, and on Hurricane Katia,
located over the southwestern Gulf of Mexico.

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

$$
Forecaster Zelinsky

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

IRMA PUMMELING THE TURKS AND CAICOS ISLANDS

Hurricane Irma Discussion Number 35
NWS National Hurricane Center Miami FL AL112017
500 PM EDT Thu Sep 07 2017

Hurricane Irma continues to have an impressive satellite
presentation with a very distinct eye. There is not much more to add
about the current intensity except that numerous data from the Air
Force reconnaissance plane indicate that the winds remain at 150
kt.

The environment along the future track of Irma is favorable for the
hurricane to maintain most of its current intensity, although some
fluctuations are likely due to eyewall replacement cycles which are
difficult to predict. There are no obvious reasons why Irma should
not remain a powerful major hurricane for the next 3 days while it
is heading for Florida or its adjacent surroundings. Thereafter, an
increase in the wind shear and the interaction with land should lead
to gradual weakening.

The best estimate of the initial motion is toward the west-northwest
or 285 degrees at 14 kt. Irma is being steered by the flow around
the south side of the subtropical ridge, but in 2 or 3 days the
hurricane is expected to be located on the southwestern edge of the
aforementioned ridge, and a turn to the northwest and north-
northwest should then begin. The forecast track for the first 2 days
was adjusted a little bit to the south given that the ridge to the
north continues to be strong, and the ECMWF and HFIP corrected
consensus (HCCA) models have shifted southward a little bit. These
two models have been performing very well during Irma. This
adjustment also results in a westward shift of the track near
Florida and northward.

KEY MESSAGES:

1. Irma is a potentially catastrophic category 5 hurricane and will
continue to bring life-threatening wind, storm surge, and rainfall
hazards to the northern coast of Hispaniola tonight. These hazards
are already spreading across the Turks and Caicos and will affect
the Bahamas tonight through Saturday. Hurricane conditions will also
spread over portions of the north coast of Cuba, especially over
the adjacent Cuban Keys through Saturday.

2. It has become more likely that Irma will make landfall in
southern Florida as a dangerous major hurricane, and bring
life-threatening storm surge and wind impacts to much of the state.
A Hurricane Watch is in effect for South Florida, the Florida Keys,
Lake Okeechobee, and Florida Bay, and will likely be expanded
northward tonight.

3. A Storm Surge Watch is in effect for portions of South Florida
and the Florida Keys. This means there is the possibility of
life-threatening inundation from rising water moving inland from the
coastline during the next 48 hours in these areas. The Potential
Storm Surge Flooding Map depicts a reasonable worst-case scenario –
the amount of inundation that has a 10 percent chance of being
exceeded. Because the Flooding Map is based on inputs that extend
through 72 hours, it best represents the flooding potential in the
watch area.

4. There is a chance of direct impacts in portions of Georgia,
South Carolina, and North Carolina, but it is too early to specify
the magnitude and location of these impacts.

FORECAST POSITIONS AND MAX WINDS

INIT 07/2100Z 20.9N 71.1W 150 KT 175 MPH
12H 08/0600Z 21.6N 73.1W 145 KT 165 MPH
24H 08/1800Z 22.2N 75.5W 140 KT 160 MPH
36H 09/0600Z 22.7N 77.6W 135 KT 155 MPH
48H 09/1800Z 23.4N 79.3W 135 KT 155 MPH
72H 10/1800Z 26.2N 80.7W 115 KT 130 MPH…INLAND
96H 11/1800Z 31.5N 82.0W 80 KT 90 MPH…INLAND
120H 12/1800Z 36.0N 84.0W 40 KT 45 MPH…INLAND

$$
Forecaster Avila

HURRICANE WATCH ISSUED FOR ST. MARTIN and SINT MAARTEN

Hurricane Jose Discussion Number 10
NWS National Hurricane Center Miami FL AL122017
Issued by the NWS Weather Prediction Center College Park MD
500 PM AST Thu Sep 07 2017

Jose has continued to develop a well-defined eye on satellite
imagery this afternoon, with the eye now established in the center
of a ring of strong convection. 18 UTC Dvorak fixes from TAFB and
SAB came in at T5.5, which suggests 100 knot intensity. However,
given the ongoing improvements in satellite presentation and CIMSS
ADT numbers which have since climbed higher, the initial intensity
for this advisory is set at 105 knots. This makes Jose a Category 3
hurricane on the Saffir-Simpson Hurricane Wind Scale. It is the
third major hurricane in the 2017 Atlantic hurricane season
(Harvey, Irma). It also means we have two major hurricanes
simultaneously in the Atlantic basin, which is not too common —
especially in such close proximity. The last time this happened was
in 2010 when Igor and Julia were both major hurricanes on September
15-16, and then Igor and Karl were both major hurricanes briefly on
September 17.

In the near-term, most factors appear aligned for continued
intensification. Outflow remains well-established in all quadrants,
and Jose has thus far not felt negative impacts from the dry air
situated just to its west and northwest. For this reason, we are
taking the intensity up to 120 knots at the 24 hour forecast point.
After that, a gradual decrease in intensity is shown, in line with
most intensity guidance. However, the intensity forecast generally
lies above most of the guidance in deference to the ongoing rapid
intensification trend. Global models do show that some of the dry
air to the west of Jose may wrap into the circulation in about
24-36 hours. That may be a contributing factor to the decrease in
intensity, as well as some increasing shear at the base of an upper
level low in the central Atlantic and perhaps the periphery of
Irma’s upper level outflow. The smaller size of Jose may make it a
little more vulnerable to effects of dry air and shear.

The initial motion remains at 285/16kt, and Jose will continue to
be steered by a well established subtropical ridge. It should not
reach the ridge axis until about 36-48 hours, at which point the
ridge begins to erode a bit and Jose may turn a bit more toward the
northwest and eventually the north. The forecast track remains very
similar to the previous official forecast through 48 hours —
roughly between the operational GFS and ECMWF and close to the
multi-model consensus. After that time, the steering flow becomes
weaker and the forward motion should slow down. Models begin to
diverge more significantly at 96hr and especially 120hr. The
forecast at these time ranges lies closer to the multi-model
consensus and the operational ECMWF than models that show a quicker
exit to the east.

FORECAST POSITIONS AND MAX WINDS

INIT 07/2100Z 15.5N 52.4W 105 KT 120 MPH
12H 08/0600Z 16.0N 54.8W 115 KT 130 MPH
24H 08/1800Z 16.6N 57.6W 120 KT 140 MPH
36H 09/0600Z 17.3N 59.8W 110 KT 125 MPH
48H 09/1800Z 18.4N 61.7W 105 KT 120 MPH
72H 10/1800Z 21.9N 65.5W 95 KT 110 MPH
96H 11/1800Z 25.5N 67.9W 80 KT 90 MPH
120H 12/1800Z 27.3N 67.2W 75 KT 85 MPH

$$
Forecaster Lamers/Carbin

KATIA MOVING LITTLE

Hurricane Katia Discussion Number 7
NWS National Hurricane Center Miami FL AL132017
400 AM CDT Thu Sep 07 2017

Katia has not changed appreciably during the past several hours
with a small central dense overcast and a curved banding feature in
the northeastern quadrant. Satellite estimates are about the same
as earlier, so the initial wind speed will stay at 70 kt. An Air
Force Reserve Hurricane Hunter aircraft is scheduled to be in the
hurricane in a few hours to get a better estimate of the current
intensity. Katia is forecast to be over very warm waters with
decreasing shear for the next 24-36 hours. Thus strengthening is
expected as long as the center remains offshore. It is still
puzzling why most of the guidance don’t intensify this much, but
since the global models continue to show significant deepening, the
official forecast will stay on the high side of the guidance.

The hurricane is essentially stationary, waiting for a ridge to
build over the northwestern Gulf to steer Katia southwestward at a
faster pace. Most of the guidance are in agreement on this track,
although the UKMET is a notable outlier showing more of a westward
motion. The only significant change from the previous advisory is
to speed up the track of Katia as it approaches the coast. Given
the latest track forecast, the government of Mexico has issued a
Hurricane Warning for the previous Hurricane Watch area.

FORECAST POSITIONS AND MAX WINDS

INIT 07/0900Z 21.5N 94.5W 70 KT 80 MPH
12H 07/1800Z 21.5N 94.5W 80 KT 90 MPH
24H 08/0600Z 21.2N 95.0W 90 KT 105 MPH
36H 08/1800Z 20.8N 95.8W 90 KT 105 MPH
48H 09/0600Z 20.2N 97.1W 70 KT 80 MPH…INLAND
72H 10/0600Z 19.5N 99.0W 15 KT 15 MPH…POST-TROP/INLAND
96H 11/0600Z…DISSIPATED

$$
Forecaster Blake

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
500 AM PDT Thu Sep 7 2017

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

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

$$
Forecaster Zelinsky
NNNN

Weather In Cayman

Synopsis

Isolated showers and thunder along with light northeasterly winds and slight seas will continue across the Cayman area for the next 24 hours as an upper level low lingers over the Northwest Caribbean. Radar images show isolated showers in and around the Cayman area moving west. At 4 am Hurricane Irma, a category 5 hurricane was located near 20.0 N and 68.3 W or about 95 miles north of Punta Cana Dominican Republic. Irma is moving towards the west-northwest at 17 mph with maximum sustained winds of 180 mph. WHILE FORECAST PATH OF HURRICANE IRMA CONTINUES TO BE OVER THE BAHAMAS, LOCAL RESIDENTS ARE ENCOURAGED TO CONTINUE TO MONITOR THE PROGRESS OF THIS SYSTEM AS IT IS STILL EXPECTED TO INFLUENCE LOCAL WEATHER CONDITIONS FROM THIS WEEKEND. THE CAYMAN ISLANDS NATIONAL WEATHER SERVICE CONTINUES TO MONITOR THIS SYSTEM AND WILL PROVIDE DETAILS ON ANY LOCAL WEATHER IMPACTS ASSOCIATED WITH THIS HURRICANE.

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

Humidity: 70% (UP from yesterday)

UV: 11.7 EXTREME (UP from yesterday)

Temperature: Today’s current temperature – See Weather Forecast Top Right of Website. Yesterday: H 92.4°F L 78.6°F

Wind direction TODAY: NNE 5-10 mph GC

Wind direction TONIGHT: N 5-10 mph GC

Barometer: 1013:00 mb Rising slowly 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 2 days 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.