Heavy Rain in Puerto Rico, August 19, 2004

PUERTO RICO AND U.S. VIRGIN ISLANDS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1120 AM AST THU AUG 19 2004

.UPDATE...THE DOPPLER RADAR AT THIS MOMENT IS SHOWING STREAMERS
DEVELOPING FROM THE ADJACENT ISLANDS AND EL YUNQUE. THE YUNQUE
STREAMER IS PRODUCING SHOWERS OVER THE SOUTHERN PORTIONS OF THE SAN
JUAN METROPOLITAN AREA. A FEW CHANGES WERE DONE ON THE MORNING GRIDS
TO REPOSITION THE MORNING WEATHER ACTIVITY.

.PREVIOUS DISCUSSION...
.SYNOPSIS...AT UPPER LEVELS...A TROUGH AT 250 MB NORTH OF PUERTO
RICO AT 23 NORTH IS MOVING SLOWLY EASTWARD AND WILL MOVE ACROSS
PUERTO RICO TODAY. A HIGH PRESSURE SYSTEM PUSHES IN FROM THE EAST
AND WILL PASS SOUTH OF THE AREA ON SUNDAY.

AT MID LEVELS...A RIDGE OF HIGH PRESSURE BUILDS IN ACROSS THE
ATLANTIC FROM THE EAST AT 23 TO 26 NORTH LATITUDE...BUT MOVES NORTH
OF 30 NORTH ON TUESDAY...AND OVER THE CONTINENTAL UNITED STATES BY
SATURDAY.

AT LOWER LEVELS...SEVERAL TROPICAL WAVES ARE IN MOTION TOWARD THE
AREA THIS MORNING. ONE WAVE AT 45 DEGREES WEST HAS POOR CONVECTION
AND IS SPREAD OVER A WIDE AREA. IT IS MOVING WEST AT ABOUT 22 KNOTS.
A SECOND WEAKER WAVE IS AT ABOUT 58 WEST. A BAND OF CONVECTION WAS
SEEN OUT AHEAD OF IT YESTERDAY BUT HAS SINCE DISSIPATED. THIS WAVE
IS MOVING SLOWER THAN THE WAVE BEHIND IT.

&&

.DISCUSSION...THE UPPER LEVEL TROUGH WAS INSTRUMENTAL IN PROVIDING
FAVORABLE CONDITIONS FOR A MOIST AND UNSTABLE ATMOSPHERE.
CONSEQUENTLY SHOWERS AND POSSIBLY A FEW THUNDERSTORMS HAVE BEEN
SCATTERED ACROSS THE RADAR MOST OF THE NIGHT. UNTIL THE TROUGH MOVES
EAST OF THE AREA TONIGHT IT IS EXPECTED TO CONTINUE FAVORING STRONG
CONVECTION. THIS WILL BE EVEN MORE ENHANCED BY THE RELATIVELY LIGHT
WINDS AT ALL LEVELS. WINDS IN THE 00Z SOUNDING DID NOT EXCEED 16
KNOTS THROUGH THE TOP OF THE SOUNDING AT 40 THOUSAND FEET.

IT IS NOT CLEAR THAT THE MODEL IS SEEING ALL OF THE MOISTURE IN THE
AREA AND THE TROPICAL WAVES TO NOT SEEM TO BE INITIALIZING AS STRONG
AS WOULD HAVE BEEN EXPECTED. MOST OF THE FEATURES THAT ARE CURRENTLY
DEPICTED ARE WASHED OUT OR SMEARED BY THE TIME THEY REACH US...SO
FORMULATING A CLEAR PICTURE WAS DIFFICULT. IT APPEARS THAT THE WEAK
WAVE AROUND 58 DEGREES WEST WILL DISSIPATE BEFORE REACHING THE AREA
ON SATURDAY...BUT WILL ENHANCE SHOWER ACTIVITY SOMEWHAT. THE SECOND
WAVE APPEARS TO ARRIVE ON SUNDAY. SINCE IT IS MOVING FASTER THAN THE
FIRST WAVE THIS SEEMS REASONABLE. IT TOO HOWEVER WILL WEAKEN
CONSIDERABLY BEFORE ARRIVING...THEREFORE NO TROPICAL SYSTEM AND NO
STRONG WAVES ARE EXPECTED IN THE NEXT 7 DAYS IN OUR FORECAST AREA.

TEMPERATURES WILL DEPEND MOSTLY ON LOCAL EFFECTS OF WHERE SHOWERS
PLAY AND NIGHTTIME CLOUDINESS...BUT SHOULD CARRY OUT WITH MOSTLY
SEASONAL NORMALS.

&&

.MARINE...AGAIN THE STRONG WINDS THAT THE GFS PUSHES THROUGH ARE
UNLIKELY...BUT HAVE ALSO BEEN REMOVED FROM SOME PERIODS IN THE MODEL
IN THE MOST RECENT RUN. THEREFORE HAVE GREATLY TEMPERED
WINDS...ESPECIALLY OVER THE OCEAN FROM THE GFS INTERPRETATION. ONLY
WITH LOWER WINDS DO THE CURRENT SEAS FORECASTS MAKE SENSE.
NEVERTHELESS THE LAST 36 HOURS OF THE FORECAST WINDS...WHICH ARE
UNDER 10 KNOTS...ARE SUSPECT AND VERY LIKELY TO CHANGE IN SUBSEQUENT
RUNS.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  89  78  89  79 /  20  40  10  40
STT  90  78  90  79 /  20  40  10  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.

&&

SNELL

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SAN JUAN PR
600 AM AST THU AUG 19 2004

PRZ001>013-AMZ710>750-201000-
600 AM AST THU AUG 19 2004

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PUERTO RICO.

.TODAY AND TONIGHT...
AN UPPER LEVEL TROUGH JUST NORTH OF THE AREA WILL COMBINE WITH THE
WEAK LOW LEVEL WIND FLOW AND MAY PRODUCE SCATTERED TO NUMEROUS
SHOWERS AND ISOLATED STRONG THUNDERSTORMS OVER MAINLY THE WEST TO
SOUTHWEST SECTIONS OF PUERTO RICO. HEAVY RAIN MOVING SLOWLY IMPLIES
A HIGHER RISK FOR SOME URBAN FLOODING MAINLY THIS AFTERNOON.

.SPOTTER CALL TO ACTION STATEMENT...
SPOTTER ACTIVATION IS NOT ANTICIPATED.

.DAYS TWO THROUGH SEVEN...
NO IMMEDIATE...ADVERSE WEATHER IS FORESEEN. DAILY SHOWER AND
THUNDERSTORMS ACTIVITY FROM THE CENTRAL INTERIOR TO THE WEST COAST
MAY PRODUCE LOCALIZED URBAN AND SMALL STREAM FLOODING. HOWEVER
...THE CURRENT AND PREDICTED WEATHER PATTERN THROUGH EARLY THIS
WEEKEND WILL NOT LIKELY YIELD ANY HAZARDOUS WEATHER IN THE FORM OF
WIDESPREAD...RAINFALL EPISODES.

VIZ001-002-AMZ710>730-201000-
600 AM AST THU AUG 19 2004

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE U.S. VIRGIN ISLANDS.

.TODAY AND TONIGHT...
INDUCED BY THE UPPER LOW NORTH OF THE AREA ISOLATED TO SCATTERED
SHOWERS ARE EXPECTED THESE ISLANDS AND THEIR SURROUNDING COASTAL
WATERS. THE SHOWERS MAY BE BRIEFLY HEAVY.

.SPOTTER CALL TO ACTION STATEMENT...
SPOTTER ACTIVATION IS NOT ANTICIPATED.

.DAYS TWO THROUGH SEVEN...
NO IMMEDIATE ADVERSE WEATHER IS FORESEEN. ISOLATED TO SCATTERED
SHOWER ACTIVITY ACROSS THE LOCAL ISLANDS IS POSSIBLE THROUGHOUT THE
THE REST OF THE WORK WEEK...MOST LIKELY AT NIGHT. HOWEVER...THE
CURRENT AND PREDICTED WEATHER PATTERN THROUGH SATURDAY WILL NOT
YIELD ANY HAZARDOUS WEATHER IN THE FORM OF WIDESPREAD...RAINFALL
EPISODES.

STAY TUNED TO NOAA WEATHER RADIO AND OTHER LOCAL MEDIA FOR FURTHER
DETAILS OR UPDATES.

FOR ADDITIONAL INFORMATION...VISIT THE NATIONAL WEATHER SERVICE WEB
SITE FOR PUERTO RICO AND THE U.S. VIRGIN ISLANDS AT (ALL LOWERCASE
LETTERS): HTTP://WWW.SRH.NOAA.GOV/SJU.

RIVERA