31 Aug Weather in Cayman & Tropical Report, 1 TS, 1 dist Gulf

August 31, 2017

Aug 31 Thursday 2017

Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Thu Aug 31 2017

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

The National Hurricane Center is issuing advisories on Tropical
Storm Irma, located over the eastern Atlantic Ocean. The Weather
Prediction Center is issuing advisories on Tropical Depression
Harvey, located over northern Louisiana.

1. An area of low pressure could form over the southwestern Gulf of
Mexico by the weekend. Development, if any, of this system is
expected to be slow to occur as the low moves slowly northward.
If this system does develop, it could bring additional rainfall to
portions of the Texas and Louisiana coasts. However, any rainfall
forecast is uncertain at this time range, and it is too soon to
determine any specific impacts. Interests in these areas should
monitor the progress of this potential system for the next few days.
* Formation chance through 48 hours…low…near 0 percent.
* Formation chance through 5 days…low…20 percent.

Public Advisories on Harvey are issued under WMO header
WTNT34 KWNH and under AWIPS header TCPAT4.

Public Advisories on Irma are issued under WMO header
WTNT31 KNHC and under AWIPS header MIATCPAT1.
Forecast/Advisories on Irma are issued under WMO header
WTNT21 KNHC and under AWIPS header MIATCMAT1.

Forecaster Blake

IRMA CLOSE TO HURRICANE STRENGTH

Tropical Storm Irma Discussion Number 4
NWS National Hurricane Center Miami FL AL112017
500 AM AST Thu Aug 31 2017

Irma continues to become better organized with a developing CDO and
a few banding features. The overall cloud pattern is fairly
symmetric, with fair upper-level outflow over all but the
southeastern portion of the circulation. The current intensity
is set at 60 kt, which is the mean of Dvorak estimates from TAFB
and SAB. The environment ahead of Irma appears to be mostly
conducive for intensification, with increasingly warm SSTs.
Vertical shear is expected to remain low as an upper-level trough
to the west-northwest of the tropical cyclone lifts out to the
north and west. The only noticeable inhibiting factor is slightly
drier mid-level air in 2-5 days, but this will probably not be much
of a deterrent for strengthening. The official intensity forecast
follows the latest consensus of the models, and is similar to the
previous NHC prediction.

Based on geostationary satellite fixes, the initial motion is just
slightly north of west or 280/10 kt. Most of the track guidance
shows a west-northwestward motion for the next day or so. Irma
will remain situated to the south of a well-defined
mid-tropospheric ridge through the forecast period. Much of the
guidance indicates that Irma will turn toward a slightly south of
westward heading in a couple of days, presumably in response to some
building of high pressure to the north and northwest. The official
track forecast also shows this, and remains on the southern side of
the guidance suite. This is mainly a blend of the GFS and ECMWF
solutions.

FORECAST POSITIONS AND MAX WINDS

INIT 31/0900Z 16.5N 32.9W 60 KT 70 MPH
12H 31/1800Z 17.0N 34.2W 70 KT 80 MPH
24H 01/0600Z 17.6N 36.0W 80 KT 90 MPH
36H 01/1800Z 18.0N 37.9W 85 KT 100 MPH
48H 02/0600Z 18.2N 40.1W 90 KT 105 MPH
72H 03/0600Z 17.5N 45.0W 100 KT 115 MPH
96H 04/0600Z 16.7N 49.5W 105 KT 120 MPH
120H 05/0600Z 16.0N 53.5W 105 KT 120 MPH

$$
Forecaster Pasch

LIDIA MOVING TOWARD THE BAJA CALIFORNIA PENINSULA… …CONDITIONS WILL DETERIORATE ACROSS SOUTHERN BAJA CALIFORNIA SUR THROUGH THE DAY

Tropical Storm Lidia Discussion Number 7
NWS National Hurricane Center Miami FL EP142017
300 AM MDT Thu Aug 31 2017

Scatterometer data and microwave images indicate that Lidia has a
deformed circulation, with what appears to be two lobes of
vorticity rotating around a common center. The unmanned NASA Global
Hawk flew very near the centroid of the circulation last evening
and provided a better estimate of Lidia’s central pressure (about
998 mb at the time). In addition, a dropsonde released to the east
of the center measured a mean boundary layer wind of 45 kt, which
equates to a surface wind a little over 35 kt. Assuming the
dropsonde did not sample the highest winds, and given that deep
convection has become more organized into two distinct clusters
since that time, the initial intensity is raised to 40 kt.

Lidia is moving north-northwestward, or 335/7 kt, between a
mid-level high centered over central Mexico and a cyclonic gyre
located to the west over the Pacific. This motion should continue
for the next 36 hours, but then after that time, high pressure over
the southwestern United States should force Lidia to turn
northwestward and west-northwestward on days 2 through 5. Most of
the spread in the track models is related to Lidia’s forward speed,
and there is a notable disparity between the faster GFS and slower
ECMWF models. The new NHC track forecast is a little faster than
the previous one to better match the speeds of the TVCN multi-model
consensus and the HFIP Corrected Consensus Approach (HCCA).

Even though Lidia is in an environment of low shear and over very
warm waters, the storm’s large size and lack of an inner core are
likely to prevent fast strengthening before the center reaches the
Baja California peninsula. Since the ambient environment is
favorable, the NHC forecast continues to call for modest
strengthening and still shows a peak intensity of 55 kt in about 24
hours, which is in line with HCCA. Weakening is expected after 24
hours due to the center moving up the spine of the Baja California
peninsula, but tropical-storm-force winds are likely to spread up
the Gulf of California well east of the center. Lidia is forecast
to become a remnant low by day 3 due to its interaction with land,
and further weakening is anticipated over the cold waters of the
California Current on days 4 and 5.

Lidia is a large system accompanied by very heavy rains which are
already occurring over portions of western Mexico and Baja
California Sur. Regardless of how strong Lidia becomes,
life-threatening flash floods and mudslides will be a significant
hazard over these areas.

FORECAST POSITIONS AND MAX WINDS

INIT 31/0900Z 21.3N 109.4W 40 KT 45 MPH
12H 31/1800Z 22.3N 109.9W 50 KT 60 MPH
24H 01/0600Z 23.6N 110.5W 55 KT 65 MPH
36H 01/1800Z 25.1N 111.4W 45 KT 50 MPH…INLAND
48H 02/0600Z 26.7N 112.6W 40 KT 45 MPH…INLAND
72H 03/0600Z 29.2N 115.9W 30 KT 35 MPH…POST-TROP/REMNT LOW
96H 04/0600Z 30.0N 119.0W 20 KT 25 MPH…POST-TROP/REMNT LOW
120H 05/0600Z 30.5N 121.5W 15 KT 15 MPH…POST-TROP/REMNT LOW

$$
Forecaster Berg

Weather In Cayman

Synopsis

Not available. See Weather Forecast Top Right of Website.

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

Humidity: 82% (Same as yesterday)

UV: 12.0 EXTREME (UP from yesterday)

Temperature: Today’s current temperature – See Weather Forecast Top Right of Website. Yesterday: H 93.5°F L 79.7°F

Wind direction TODAY: ESE 10-15 mph GC

Wind direction TONIGHT: ESE 5-10 mph GC

Barometer: 1015:00 mb Steady Rain: Last month: 6.69 in Last 24 hrs 0.00 This month: 4.27 in

12 Rain days in July 15 Rain days in Aug 3 days since rain

2016 Season Total: 20.23 in 2017 Season Total: 23.38 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.