9 Sep Weather in Cayman & Tropical Report, 2 H-canes, 1 TD [IRMA 11pm UPDATE]

September 9, 2017

Sep 9 Sat 2017

Tropical Report

Tropical Weather Outlook…Corrected
NWS National Hurricane Center Miami FL
800 AM EDT Sat Sep 9 2017

Corrected to reflect that Katia is a Tropical Depression.

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

The National Hurricane Center is issuing advisories on Hurricane
Irma, located near the coast of central Cuba, on Hurricane Jose,
located a couple of hundred miles east of the Leeward Islands, and
on Tropical Depression Katia, located inland over eastern Mexico.

1. A tropical wave located several hundred miles southeast of the Cabo
Verde Islands is producing disorganized showers and thunderstorms.
This activity has increased since yesterday, and some gradual
development of this system is possible during the next few days
while it moves west-northwestward over the eastern Atlantic Ocean.
* Formation chance through 48 hours…low…10 percent.
* Formation chance through 5 days…low…30 percent.

IRMA TAKING ITS TIME MOVING AWAY FROM CUBA… …LIFE-THREATENING STORM SURGE EXPECTED IN THE FLORIDA KEYS AND THE WEST COAST OF FLORIDA

Hurricane Irma Discussion Number 44
NWS National Hurricane Center Miami FL AL112017
1100 PM EDT Sat Sep 09 2017

Irma’s nearly 24-hour traversal of the north coast of Cuba appears
to have affected the hurricane’s structure and intensity. An
earlier NOAA Hurricane Hunter aircraft and a more recent Air Force
reconnaissance flight both measured maximum flight-level winds near
105 kt and surface winds near 95 kt. The planes have reported
a double eyewall structure, which has also been observed in WSR-88D
Doppler radar data from Miami and Key West. Irma’s intensity has
been conservatively lowered to 105 kt, and I’d rather wait to lower
the winds further until we’ve seen the full data set from the Air
Force mission.

Irma has stuttered near the north coast of Cuba for the past few
hours, which may be a harbinger of the north-northwestward turn
that we’ve been waiting for. In any event, Irma appears to be
moving very slowly toward the northwest, or 305/5 kt, very gradually
shifting away from the north coast of Cuba. With the hurricane
located near a break in the subtropical ridge, it should turn
north-northwestward soon and accelerate near or along the west
coast of Florida during the next 36-48 hours. Because of Irma’s
hesitation to move northwestward, the new track guidance has shifted
ever so slightly westward, and the new NHC track is just a little
left of the previous one. Although it is likely that the eye will
move near or over the Lower Keys Sunday morning, the hurricane’s
angle of approach to the west coast of Florida makes it very
difficult to pinpoint exactly where Irma will cross the Florida Gulf
coast.

If an eyewall replacement occurs within the next 6-12 hours, Irma
has an opportunity to restrengthen a bit while it moves across the
Straits of Florida. After that time, however, southwesterly shear
is expected to increase to 25-30 kt in about 24 hours and then
continue increasing through 48 hours. This shear, in addition to
Irma’s core interacting with Florida, is likely to cause a
weakening trend after 24 hours. The new intensity guidance calls
for an adjustment from the previous forecast, although it
conservatively lies near the upper bound of the reliable models.
Irma is still expected to approach the Florida Keys and Florida
west coast as a major hurricane, and combined with its large size,
will produce significant storm surge flooding in those areas.

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 tonight through Sunday. Preparations in the Florida
Keys and southwest Florida should be complete since tropical-storm-
force winds are already affecting portions of the coast.

2. There is an imminent danger of life-threatening storm surge
flooding in portions of central and southern Florida, 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, and
everyone in these areas should immediately follow any evacuation
instructions from local officials.

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 10 to 20 inches, with isolated amounts
of between 20 and 25 inches, are expected over the Florida Keys, the
Florida peninsula, and southeast Georgia from Saturday through
Monday. Significant river flooding is possible in these areas. Early
next week Irma will also bring periods of heavy rain to much of the
southeast United States where an average of 2 to 6 inches is
forecast, with isolated higher amounts, from North and South
Carolina to Tennessee and eastern Alabama. 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 10/0300Z 23.5N 81.0W 105 KT 120 MPH
12H 10/1200Z 24.7N 81.7W 110 KT 125 MPH
24H 11/0000Z 26.8N 82.4W 105 KT 120 MPH
36H 11/1200Z 29.5N 83.4W 80 KT 90 MPH…ON THE COAST
48H 12/0000Z 32.2N 85.0W 55 KT 65 MPH…INLAND
72H 13/0000Z 35.3N 89.0W 25 KT 30 MPH…POST-TROP/INLAND
96H 14/0000Z 37.0N 88.5W 20 KT 25 MPH…POST-TROP/INLAND
120H 15/0000Z…DISSIPATED

JOSE A LITTLE WEAKER BUT STILL A DANGEROUS CATEGORY 4 HURRICANE

Hurricane Jose Discussion Number 16
NWS National Hurricane Center Miami FL AL122017
500 AM AST Sat Sep 09 2017

There has been some weakening of the inner core this morning,
specifically, considerable warming of the cloud tops and partial
erosion of the western portion of the eyewall. Indications
from earlier microwave passes and radar imagery from the Leeward
Island of Guadeloupe reveal the possibility of an ongoing eyewall
replacement cycle (ERC). Subsequently, the initial intensity is
generously lowered to 130 kt for this advisory. An aircraft
reconnaissance mission later this morning will provide a more
accurate measure of Jose’s intensity.

Whether or not Jose completes the ERC cycle during the next several
hours is uncertain. Regardless of the inner core structural
transition, Jose is still forecast to be a category 4 hurricane as
it closely approaches the northern Leeward Islands today.
Statistical and dynamical intensity guidance show gradual weakening
of the cyclone through day 5 as a result of increasing northerly
shear and drier, more stable mid-tropospheric air associated with an
approaching mid-latitude trough to the northwest of the cyclone.
The official forecast is above all of the available guidance through
24 hours, then corresponds to the IVCN multi-model consensus.

The initial motion is estimated to be west-northwestward, or 300/11
kt. The eye of Jose is expected to turn northwestward and pass
just east of the northern Leeward Islands later today. Jose should
slow down and turn north-northwestward in 72 hours in response to
the aforementioned deep-layer mid-level trough. Large-scale
models have come in alignment with the trough leaving Jose behind to
meander in weaker mid-level westerly flow through day 5. The NHC
forecast is basically an update of the previous package and is based
on a blend of the HFIP Corrected Consensus model and the ECMWF.

FORECAST POSITIONS AND MAX WINDS

INIT 09/0900Z 17.5N 60.3W 130 KT 150 MPH
12H 09/1800Z 18.4N 61.8W 125 KT 145 MPH
24H 10/0600Z 19.9N 63.9W 115 KT 130 MPH
36H 10/1800Z 21.5N 65.9W 110 KT 125 MPH
48H 11/0600Z 23.1N 67.6W 100 KT 115 MPH
72H 12/0600Z 25.7N 69.0W 90 KT 105 MPH
96H 13/0600Z 26.5N 67.6W 80 KT 90 MPH
120H 14/0600Z 26.4N 66.3W 80 KT 90 MPH

$$
Forecaster Roberts

KATIA WEAKENS TO A DEPRESSION NEAR THE SIERRA MADRE MOUNTAINS… …HEAVY RAINFALL THREAT CONTINUES

Tropical Storm Katia Discussion Number 15
NWS National Hurricane Center Miami FL AL132017
Issued by the NWS Weather Prediction Center College Park MD
400 AM CDT Sat Sep 09 2017

Convection has substantially diminished with Katia, with satellite
imagery showing a significantly degraded structure. In fact, it
seems that the low-level circulation may be decoupled from the
low center aloft now, as a distinct circulation in diminishing
colder cloud tops moved more quickly off to the southwest. There was
already evidence of this occurring from the recon flight earlier
tonight. The initial position was determined via the circulation in
warmer clouds in the lower troposphere on IR satellite. Katia is
very close to the higher terrain of the Sierra Madre Mountains, and
thus the forecast shows very little movement this morning as the
increasingly shallow circulation would be less likely to propagate
west through the mountainous areas.

The initial intensity is set at 35 knots out of respect for the
hurricane strength Dvorak fixes only nine hours ago, and the extent
of tropical storm force winds sampled by the recon plane shortly
thereafter, although this could be generous. The most likely
location of tropical storm force winds would be away from the center
and over the water or near the coast in the eastern semicircle of
Katia’s circulation. The wind field should continue to weaken this
morning, and we show a dissipation of Katia by 18Z today.

Although convection has generally diminished as of 09Z, lingering
elevated levels of atmospheric moisture associated with Katia could
continue to produce heavy rains in the region, which could lead to
flash floods and mudslides even after Katia dissipates.

FORECAST POSITIONS AND MAX WINDS

INIT 09/0900Z 20.3N 97.5W 35 KT 40 MPH
12H 09/1800Z 20.2N 97.6W 20 KT 25 MPH…INLAND
24H 10/0600Z…DISSIPATED

$$
Forecaster Lamers/Roth

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
500 AM PDT Sat Sep 9 2017

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

1. An area of low pressure is expected to form well south of the Baja
California peninsula by the middle of next week. Environmental
conditions are expected to be favorable for gradual development
after that time.
* Formation chance through 48 hours…low…0 percent.
* Formation chance through 5 days…low…20 percent.

Forecaster Zelinsky

Weather In Cayman

WHILE FORECAST PATH OF HURRICANE IRMA HAS THE SYSTEM MOVING AWAY FROM OUR AREA FROM THIS MORNING, RESIDENTS ARE ENCOURAGED TO CONTINUE TO MONITOR THE PROGRESS OF THIS HURRICANE AS IT IS EXPECTED TO CONTINUE INFLUENCE LOCAL WEATHER CONDITIONS THROUGHOUT THE 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.

Synopsis

Cloudiness and thundershowers along with fresh to strong westerly to southwesterly winds and rough seas is expected to continue through the next 24 hours as Hurricane Irma moves towards Florida. Radar images show scattered showers mainly over the Sister Islands, moving south.

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

Humidity: 77% (DOWN from yesterday)

UV: 11.8 EXTREME (DOWN from yesterday)

Temperature: Today’s current temperature – See Weather Forecast Top Right of Website. Yesterday: H 90.4°F L 81.0°F

Wind direction TODAY: W 25-35 mph GC

Wind direction TONIGHT: WSW 20-30 mph GC

Barometer: 1005:00 mb Steady Rain: Last month: 4.29 in Last 24 hrs 0.26 This month: 1.90 in

16 Rain days in Aug 5 Rain days in Sep 0 days since rain

2016 Season Total: 20.23 in 2017 Season Total: 25.34 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.