#1755 Postby cycloneye » Mon Aug 24, 2009 2:30 pm
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
312 PM AST MON AUG 24 2009
.SYNOPSIS...AT UPPER LEVELS...A STRONG UPPER LEVEL LOW IS NORTH OF
SAINT MARTIN BUT IS RETREATING NORTH. A WEAKER LOW WILL FORM AT
THE BASE OF THIS LOW TONIGHT AND MOVE WEST SOUTHWEST AT ABOUT 10
KNOTS...AND WILL BE OVER HAITI BY WEDNESDAY MORNING. DURING THE
REST OF THE WEEK HIGH PRESSURE WILL FORM TO THE NORTH...BUT
ANOTHER WEAK LOW WILL ALSO FORM TO THE NORTHEAST BY THE WEEKEND.
AT MID LEVELS...HIGH PRESSURE REMAINS ANCHORED ACROSS THE ATLANTIC
MOVING AROUND 35 NORTH 50 WEST UNTIL NEXT WEEK. A TROUGH OVER THE
EASTERN CARIBBEAN TODAY WILL MOVE WEST...A WEAK LOW WILL FORM IN
THE APEX OF THE TROUGH NORTH OF PUERTO RICO AND MOVE NORTHWEST
TUESDAY THROUGH THURSDAY. TROUGHING IN THE MID TROPICAL ATLANTIC
TODAY WILL MOVE WEST ACROSS THE LOCAL AREA SATURDAY NIGHT AND
SUNDAY...WITH HIGH PRESSURE FOLLOWING.
AT LOWER LEVELS...A TROPICAL WAVE WILL MOVE INTO AN AREA ALREADY
ACTIVE WITH CONVECTION FROM THE UPPER LEVEL LOW TUESDAY MORNING.
MOISTURE WILL STREAM INTO THIS SYSTEM THROUGH WEDNESDAY MORNING
KEEPING THE LOCAL AREA WET. MOISTURE RETURNS THURSDAY THROUGH
SATURDAY...AND ANOTHER TROPICAL WAVE MOVES INTO THE AREA ON MONDAY
NEXT WEEK.
&&
.DISCUSSION...GOOD MOISTURE WITH PRECIPITABLE WATER MOVING UP
THROUGH TWO INCHES HAS REACTED TO THE STRONG DAYTIME HEATING AND AN
UNSTABLE SOUNDING AND PRODUCED SCATTERED THUNDERSTORMS WITH
FREQUENT AND COPIOUS LIGHTNING. SOME RAIN AMOUNTS HAVE EXCEEDED 3
INCHES IN MARICAO ACCORDING TO NWS RADAR AND SEVERAL FLS`S HAVE
BEEN ISSUED.
THE WAVE IS STILL BEING STRONGLY DEVELOPED BY THE NAM AND THE
FORECAST THAT IT IS PRODUCING IS STRONGLY DISTORTED BY THIS
CYCLOGENESIS TO OUR NORTH. THEREFORE HAVE HAD TO RELY ALMOST
COMPLETELY ON THE GFS. BOTH MODELS RIGHTLY BRING AND KEEP PRECIPITATION
MAXIMUMS TO OUR NORTH AND THIS IS WHERE THE HEAVIEST RAINFALL WILL
BE. EXPECT CONSIDERABLE ACTIVITY INCLUDING THUNDERSTORMS ACROSS
PUERTO RICO BEGINNING TONIGHT AND CONTINUING THROUGH EARLY
WEDNESDAY AND POSSIBLY BEYOND DEPENDING ON HOW MUCH THE LOW
PRESSURE DEVELOPS TO OUR NORTH. ALSO THE TRANSLATION OF THE UPPER
LEVEL LOW TO THE WEST SOUTHWEST WILL BE QUITE FAVORABLE FOR
THUNDERSTORMS AND GOOD ACTIVITY TUESDAY. SOME FLOODING MAY BE
POSSIBLE BUT IT IS STILL TOO EARLY TO TELL WHERE. SURFACE WINDS
TUESDAY WERE SOUTHEAST TO SOUTH SOUTH EAST IN THE MODEL RUNS AND
THE EXACT DIRECTION WILL BE CRITICAL. THE GFS ALSO NOTES GOOD
MOISTURE AT 700 MB BEGINNING THURSDAY AFTER THIS SYSTEM PASSES SO
CANNOT RULE OUT A FAIRLY MOIST SERIES OF AFTERNOONS THURSDAY
THROUGH SATURDAY.
&&
.AVIATION...OVERALL VFR CONDITIONS ARE EXPECTED ACROSS THE LOCAL TAF
SITES FOR THE NEXT 18 TO 24 HOURS. HOWEVER...TJMZ MAY EXPERIENCE
BRIEF MVFR CONDITIONS AS SHOWERS AND THUNDERSTORMS MOVE ACROSS THE
AIRPORT BETWEEN 19Z TO 21Z. LATER TONIGHT INTO THE OVERNIGHT
HOURS...U.S. VIRGIN ISLANDS TAF SITES...AND TNCM AND TKPK MAY
ALSO EXPERIENCE BRIEF MVFR AND EVEN IFR CONDITIONS AS SQUALL LINES
MOVES ACROSS THE EASTERN CARIBBEAN TOWARD THE EAST...RESULTING IN
LOW VISIBILITIES AND CEILINGS AS WELL AS MOUNTAIN OBSCURATIONS.
&&
.MARINE...SEAS ARE EXPECTED TO HOLD AT JUST 7 FEET IN THE
NORTHEAST PORTION OF THE FORECAST AREA FOR THE NEXT 30 OR SO
HOURS. THEN EXPECT SEAS TO DIE DOWN A BIT. WINDS SHOULD BE MINIMAL
ON TUESDAY AND THEN RETURN CLOSER TO SEASONAL NORMALS.
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