044
FXCA20 KWBC 061254
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
854 AM EDT THU APR 06 2023
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM APR
06/12UTC: TODAY IS EXPECTED TO BE ACTIVE...WITH SHOWERS AND
THUNDERSTORMS IN AND AROUND THE USVI AND PR...WITH A RISK OF
SQUALLS. OUR FORECAST FOR MAX RAINFALL TODAY IS UNDER 2.5 INCHES
ACROSS EASTERN PR...BUT ISOLATED HIGHER AMOUNTS ARE EXPECTED. THAT
SAID...THE ECMWF MODEL GUIDANCE IS SUGGESTING UPWARDS OF 4 INCHES
OF RAIN ACROSS EASTERN PR. WE DECIDED TO STAY CLOSER TO THE
CONSENSUS OF THE REST OF THE MODEL GUIDANCE...AS THE ECMWF HAD A
RELATIVELY LARGE COVERAGE AREA WITH THE HIGH RAINFALL FORECAST.
FRIDAY WILL BE ACTIVE AS WELL THOUGH NOT EXPECTED TO BE AS MUCH AS
TODAY...AND SATURDAY LESS ACTIVE THAN FRIDAY. THE FORECAST FOR
THIS LATTER PART OF THE WORKWEEK HAS REMAINED ESSENTIALLY
UNCHANGED FROM THE PREVIOUS DISCUSSIONS. THE TOTAL PRECIPITABLE
WATER IS ABOVE NORMAL...ROUGHLY IN THE 75TH PERCENTILE AND WILL
CONTINUE TO BE NEAR THAT FOR THE NEXT SEVERAL DAYS. AT THE SURFACE
THERE IS A HIGH PRESSURE MOVING INTO THE CENTRAL ATLANTIC...WHICH
WILL KEEP A GENERALLY EASTERLY WIND FLOW UNTIL SUNDAY...WHEN A
SURFACE LOW ENTERS THE SOUTHWEST ATLANTIC AND CAUSES THE LOCAL
WINDS TO SHIFT TO A SOUTHEASTERLY DIRECTION FOR THE FIRST FEW DAYS
OF NEXT WEEK. IN THE MID LEVELS...THERE IS A LOW PRESSURE CENTERED
OVER PR/USVI...WHICH WILL MEANDER OVER THE AREA UNTIL
SATURDAY...WEAKENING AND FLATTENING BY SUNDAY. IN THE UPPER
LEVELS...A TUTT WILL STRENGTHEN AND WILL BE CENTERED TO THE
WEST-NORTHWEST OF PR TODAY AND FRIDAY...ALSO WEAKENING ON SATURDAY
AND FLATTENING ON SUNDAY. THIS STRONG TUTT WILL CAUSE A SURFACE
INDUCED TROUGH TODAY AND FRIDAY. THIS PATTERN WILL CAUSE
SIGNIFICANT INSTABILITY OVER THE LOCAL AREA...ESPECIALLY TODAY.
THE 500MB TEMPERATURES WERE OBSERVED TO BE NEARLY -13C...WHICH IS
MUCH COLDER THAN NORMAL...AND WILL REMAIN THIS COLD ON FRIDAY AS
WELL. THE 700-500MB RELATIVE HUMIDITY WILL ALSO BE OVER 2 STANDARD
DEVIATIONS ABOVE NORMAL THROUGH FRIDAY...AND THE 700-500MB LAPSE
RATES WILL BE ALSO ABOVE NORMAL TODAY...THOUGH DECREASING TO NEAR
NORMAL ON FRIDAY. BECAUSE OF ALL THIS...THE LATEST ENHANCED
GALVEZ-DAVISON INDEX (EGDI) CONTINUES TO SUGGEST THE POSSIBILITY
OF SCATTERED THUNDERSTORMS TODAY...WITH EASTERN PR AND THE USVI
SHOWING THE STRONGEST SIGNAL OF INSTABILITY. THE INDEX DECREASES
DURING THE NIGHT...BUT WILL INCREASE ONCE AGAIN ON
FRIDAY...SUGGESTING THE POSSIBILITY OF ISOLATED TO SCATTERED
THUNDERSTORMS ACROSS THE EASTERN SECTIONS OF PR AND INTO THE USVI.
IN TERMS OF FORECAST AMOUNTS...TODAY AND FRIDAY...DUE TO THE
EXPECTED THUNDERSTORM ACTIVITY...MODELS CONTINUE TO SUGGEST A
SIGNIFICANT AMOUNT OF RAIN TO BE OBSERVED...ESPECIALLY FOR EASTERN
PR...SOME NORTHERN AREAS OF PR AS WELL...AND THE USVI. THE ECMWF
IS THE MOST AGGRESSIVE MODEL SUGGESTING UPWARDS OF 4 INCHES OF
RAIN FOR TODAY...BUT THE GFS HAS LESS RAINFALL IN THE
FORECAST...AND THE NBM EVEN LESS SO...PEAKING AT AROUND 2 -2.5
INCHES OR SO. HOWEVER THERE IS NO DOUBT THAT THERE IS SOME
AGREEMENT THAT SIGNIFICANT RAINFALL WILL OCCUR TODAY INTO
FRIDAY...AND THAT ISOLATED AMOUNTS OF OVER 2 INCHES ARE VERY
POSSIBLE TODAY. CONSIDERING THE INSTABILITY...THERE WOULD ALSO BE
A RISK OF SQUALLY WEATHER WITH THE STRONG THUNDERSTORMS. A
DECREASING THUNDERSTORM TREND IS STILL EXPECTED STARTING ON FRIDAY
EVENING. HOWEVER...SHOWERS AND THUNDERSTORMS ARE STILL FORECAST
FOR THE WEEKEND...ESPECIALLY ON SATURDAY...BUT MUCH MUCH LESS
RAINFALL ACCUMULATION IS EXPECTED.
ALAMO/ACOSTA...WPC (USA)
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