Statement as of 11:00 am AST on August 21, 2011
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...Irene expected to strengthen and pass near Puerto Rico tonight...
summary of 1100 am AST...1500 UTC...information
-----------------------------------------------
location...17.0n 63.2w
about 235 mi...375 km ESE of Ponce Puerto Rico
maximum sustained winds...50 mph...85 km/h
present movement...WNW or 285 degrees at 20 mph...32 km/h
minimum central pressure...1005 mb...29.68 inches
watches and warnings
--------------------
changes in watches and warnings with this advisory...
the Tropical Storm Warning for Puerto Rico...Vieques...and Culebra
is changed to a Hurricane Warning.
A Hurricane Watch has been issued for the U.S. Virgin Islands.
The government of the Dominican Republic has changed the Tropical
Storm Warning to a Hurricane Warning for the north coast of the
Dominican Republic from Cabo engano to Cabo Frances Viejo.
The tropical storm watch for Haiti is changed to a Tropical Storm
Warning.
The government of the Bahamas has issued a tropical storm watch for
the southeastern Bahamas and the Turks and Caicos Islands.
Summary of watches and warnings in effect...
a Hurricane Warning is in effect for...
* Puerto Rico...Vieques...and Culebra
* the Dominican Republic from the southern border with Haiti to Cabo
Frances Viejo on the north coast
a Hurricane Watch is in effect for...
* U.S. Virgin Islands
a Tropical Storm Warning is in effect for...
* U.S. Virgin Islands
* Saba...St. Eustatius...St. Maarten...St. Martin...and St.
Barthelemy
* Antigua...Barbuda...St. Kitts...Nevis...Anguilla...Montserrat
* British Virgin Islands
* northern coast of the Dominican Republic from the Haiti border
eastward to Cabo Frances Viejo
* Haiti
a tropical storm watch is in effect for...
* southeastern Bahamas and the Turks and Caicos Islands
for storm information specific to your area in the United
States...please monitor products issued by your local National
Weather Service forecast office. For storm information specific to
your area outside the United States...please monitor products
issued by your National meteorological service.
Discussion and 48-hour outlook
------------------------------
at 1100 am AST...1500 UTC...the center of Tropical Storm Irene was
located near latitude 17.0 north...longitude 63.2 west. Irene is
moving toward the west-northwest near 20 mph...32 km/h...and this
motion is expected to continue for the next couple of days with a
gradual decrease in forward speed. On the forecast track...Irene
will pass near Puerto Rico tonight or early Monday and approach the
Dominican Republic on Monday.
Maximum sustained winds are near 50 mph...85 km/h...with higher
gusts. Some strengthening is forecast during the next day or
so...and Irene could become a hurricane on Monday.
Tropical-storm-force winds extend outward up to 150 miles...240
km...mainly to the north of the center.
An Air Force hurricane hunter aircraft reported a minimum central
pressure of 1007 mb...29.74 inches.
Hazards affecting land
----------------------
wind...tropical storm conditions are expected in the Leeward Islands
today. Tropical storm conditions are expected to begin this
afternoon in the Virgin Islands and Puerto Rico...and in the
Dominican Republic early Monday. Hurricane conditions are
expected over Puerto Rico...Vieques...and Culebra tonight...and over
the Dominican Republic on Monday.
Rainfall...Irene is expected to produce total rainfall accumulations
of 4 to 7 inches in the Leeward Islands...Puerto Rico and the
Virgin Islands...with isolated maximum amounts of up to 10 inches.
Total rainfall accumulations of 6 to 10 inches are possible across
the Dominican Republic and Haiti...with isolated maximum amounts of
20 inches possible. These rains could cause life-threatening flash
floods and mud slides in areas of steep terrain.
Storm surge...a storm surge will raise water levels by as much as 3
to 5 feet above normal tide levels along the coast of the Dominican
Republic in the Hurricane Warning area. A storm surge of 1 to 3
feet above normal tide levels is expected along the coast of Puerto
Rico...as well as in the Tropical Storm Warning area. Near the
coast...the surge will be accompanied by large and dangerous waves.
Next advisory
-------------
next intermediate advisory...200 PM AST.
Next complete advisory...500 PM AST.
$$
Forecaster Pasch
Statement as of 11:00 am AST on August 21, 2011
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the cloud pattern of Irene is characterized by well-defined deep
convective banding features over the northern semicircle. The storm
still lacks much deep convection...or strong winds...over the
southern portion of the circulation. An Air Force hurricane hunter
aircraft investigating Irene measured peak 850 mb flight-level
winds of 53 kt so far...which supports keeping the intensity at 45
kt for this advisory. Since an upper-level anticyclone is
established over the tropical cyclone and the system will be moving
over warm waters...intensification seems likely and Irene is
forecast to become a hurricane by the time it reaches Hispaniola.
After that...the intensity forecast is subject to more than the
usual level of uncertainty...as it depends very much on how Irene
will interact with the mountainous land masses of Hispaniola and
eastern Cuba over the next few days. If the center moves more over
the water than indicated in the current forecast...Irene will
likely become stronger than shown here.
The storm is being steered west-northwestward...285/17...by the flow
on the south side of a mid-level subtropical ridge over the western
Atlantic. Over the next few days...a couple of troughs are forecast
to create a weakness in the ridge near the southeast U.S.
Coast...which should induce a turn toward the northwest. There is a
fair amount of spread in the track guidance models...especially at
days 4 to 5. For example...the GFDL model takes Irene to the west
of the Florida Peninsula while the HWRF model takes it through the
northwestern Bahamas. Interests in Florida are advised not to focus
on the exact forecast track because of the inherent uncertainties
in longer-range forecasts.
Forecast positions and Max winds
init 21/1500z 17.0n 63.2w 45 kt 50 mph
12h 22/0000z 17.5n 65.5w 55 kt 65 mph
24h 22/1200z 18.2n 68.2w 65 kt 75 mph
36h 23/0000z 18.9n 70.9w 50 kt 60 mph...inland
48h 23/1200z 19.6n 73.3w 45 kt 50 mph...inland
72h 24/1200z 21.5n 76.5w 50 kt 60 mph...over water
96h 25/1200z 24.0n 79.0w 65 kt 75 mph
120h 26/1200z 27.0n 81.5w 50 kt 60 mph...inland
$$
forecaster Pasch
