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Tropical storm warnings issued for Potential Tropical Cyclone Two

Posted by Chris in Tampa on 6/18/2017, 4:59 pm

Not yet a depression or tropical storm and for the first time advisories are written so a tropical storm warning can be issued.

Still waiting for graphical track.





"Potential Tropical Cyclone Two Discussion Number   1
NWS National Hurricane Center Miami FL       AL022017
500 PM AST Sun Jun 18 2017

The disturbance over the deep tropical Atlantic has become better
organized today, although a pair of ASCAT-A and B passes this
morning indicated that the system does not have a closed low-level
circulation, which isn't surprising given the fast translational
speed of the system.  The ASCAT passes showed peak winds of near
30 kt well north of the center, and given that the environment is
expected to be conducive for some additional development before the
shear increases in the eastern Caribbean Sea, strengthening is
forecast, and the disturbance is expected to become a tropical storm
before reaching the Windward Islands in 36 to 48 hours.

The National Hurricane Center now has the option to issue advisories
on disturbances that are not yet tropical cyclones, but which pose
the threat of bringing tropical storm or hurricane conditions to
land areas within 48 hours. Under previous policy this was not
possible. These systems are known as Potential Tropical Cyclones in
advisory products and are numbered from the same list as
depressions. Because of the threat to the Windward Islands,
advisories have been initiated on Potential Tropical Cyclone Two and
the appropriate warnings have been issued by the respective
governments in the Windward Islands. Advisory packages will continue
until the threat of tropical-storm-force winds for land areas
sufficiently diminishes, although if the system becomes a tropical
cyclone, the normal rules for discontinuing advisories would apply.
Users should be aware that forecast uncertainty for disturbances is
generally larger than for tropical cyclones, especially beyond 48-72
hours.

The disturbance will be steered quickly westward to west-
northwestward over the next several days to the south of a mid-level
subtropical ridge over the central Atlantic.  The NHC track
forecast is close to a blend of the latest GFS and ECMWF tracks.
There is a fair bit of across-track spread in the model guidance,
which isn't surprising given the lack of a well-defined center.
However, given that tropical storm conditions are expected to extend
well north of the center, users should not focus on the exact track
of the center, and the track forecast is of lower certainty than
usual.

Most of the intensity guidance shows mostly modest strengthening
during the next 36 hours, with the system moving over SSTs of 27-28C
and the deep-layer shear at 10 kt or less.  The NHC forecast shows
the system peaking at 45 kt, in agreement with the intensity model
consensus.  Quick weakening is expected after that time as southerly
shear increases dramatically while the system moves into the eastern
Caribbean Sea. The system is forecast to become a remnant low by 72
hours and dissipate by day 4.

FORECAST POSITIONS AND MAX WINDS

INIT  18/2100Z  7.5N  50.4W   30 KT  35 MPH...POTENTIAL TROP CYCLONE
12H  19/0600Z  8.2N  53.3W   30 KT  35 MPH
24H  19/1800Z  9.5N  57.0W   35 KT  40 MPH...TROPICAL CYCLONE
36H  20/0600Z 10.6N  60.5W   45 KT  50 MPH
48H  20/1800Z 11.9N  64.0W   40 KT  45 MPH
72H  21/1800Z 13.5N  71.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
96H  22/1800Z...DISSIPATED

$$
Forecaster Brennan"





"Potential Tropical Cyclone Two Advisory Number   1
NWS National Hurricane Center Miami FL       AL022017
500 PM AST Sun Jun 18 2017

...TROPICAL STORM WARNING ISSUED FOR PORTIONS OF THE WINDWARD
ISLANDS...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...7.5N 50.4W
ABOUT 815 MI...1310 KM ESE OF THE WINDWARD ISLANDS
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 23 MPH...37 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:

The government of Barbados has issued a Tropical Storm Warning for
Barbados, St. Vincent, and the Grenadines.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Tropical Storm Warning is in effect for...
* Barbados
* St. Vincent and the Grenadines

A Tropical Storm Warning means that tropical storm conditions are
expected somewhere within the warning area within 36 hours.

For storm information specific to your area, please monitor
products issued by your national meteorological service.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
At 500 PM AST (2100 UTC), the disturbance was centered near latitude
7.5 North, longitude 50.4 West.  The system is moving toward the
west near 23 mph (37 km/h).  A fast motion toward the west-
northwest is expected to continue for the next 48 hours.  On the
forecast track, the disturbance is expected to move through the
Windward Islands Monday night and Tuesday.

Maximum sustained winds are near 35 mph (55 km/h) with higher gusts.
Some strengthening is forecast during the next 48 hours, and the
disturbance is expected to reach tropical storm intensity on Monday
before it reaches the Windward Islands.

Shower and thunderstorm activity associated with the disturbance
has become better organized since yesterday, and some additional
development is possible during the next couple of days before
conditions become less favorable for tropical cyclone formation
over the Caribbean Sea.
* Formation chance through 48 hours...high...70 percent
* Formation chance through 5 days...high...70 percent

The estimated minimum central pressure is 1008 mb (29.77 inches).


HAZARDS AFFECTING LAND
----------------------
WIND:  Tropical storm conditions are expected to first reach the
warning area overnight Monday and Tuesday morning, making outside
preparations difficult or dangerous.

RAINFALL:  The disturbance is expected to produce total rain
accumulations of 2 to 4 inches over the Windward Islands Monday
through Tuesday.


NEXT ADVISORY
-------------
Next intermediate advisory at 800 PM AST.
Next complete advisory at 1100 PM AST.

$$
Forecaster Brennan"



http://www.nhc.noaa.gov/#Two

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Potential Tropical Cyclone Two - cypresstx, 6/18/2017, 4:29 pm

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