#29 Postby cycloneye » Thu May 12, 2005 3:21 pm
000
FXCA62 TJSJ 121959
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
358 PM AST THU MAY 12 2005
.SYNOPSIS...AT UPPER LEVELS...A PERSISTENT EAST TO WEST JET AT 250
MB OF 80-100 KNOTS WILL OSCILLATE BETWEEN 21 AND 28 NORTH DURING THE
NEXT 10 DAYS. AREAS OF DIVERGENCE...SOME STRONG...WILL PUSH ACROSS
PUERTO RICO AND THE U.S. VIRGIN ISLANDS.
AT MID LEVELS...WEST SOUTHWEST FLOW WILL CONTINUE OVER THE AREA THE
ENTIRE PERIOD.
AT LOWER LEVELS...AN OLD FRONTAL BOUNDARY THAT SETTLED OVER THE AREA
FOR THE LAST TWO TO THREE DAYS WILL LIKELY REMAIN IN THE AREA FOR
THE NEXT 7 DAYS. A LOW PRESSURE ORIGINATING NEAR CENTRAL AMERICA IS
FORECAST TO MOVE ACROSS HISPANIOLA AND TO THE NORTHEAST. AS IT
PASSES NORTH OF THE AREA WEDNESDAY OR THURSDAY NEXT...IT SHOULD PUSH
THE TROUGH OVER THE AREA TO THE SOUTH. AN EASTERLY WAVE IS TILTED
FROM 10 N 61 WEST TO 15 N 56 WEST AND WILL BECOME EVEN MORE
POSITIVELY TILTED. IT IS NOW EXPECTED TO DISSIPATE LATE TOMORROW AND
SATURDAY.
&&
.DISCUSSION...FLOW ALOFT OVER PUERTO RICO IS EAST SOUTHEAST TO
SOUTHEAST BELOW 10 THOUSAND FEET AND WESTERLY ABOVE. PRECIPITABLE
WATER HAS AGAIN PUSHED ABOVE 2 INCHES AND THE SOUNDING IS FAIRLY
MOIST UP THROUGH 400 MB. RADAR SHOWS A BAND OF LIGHT TO MODERATE
RAIN STRETCHED WEST SOUTHWEST TO EAST NORTHEAST ACROSS PUERTO RICO
WITH CELLS GENERALLY MOVING ALONG THE BAND TO THE EAST NORTHEAST.
HOWEVER SHOWERS AND THUNDERSTORMS THAT FORM BOTH SOUTHEAST OF PUERTO
RICO AND TO THE NORTH ARE MOVING ALMOST DUE WEST WHILE MOST OF THEIR
MID LEVELS ARE MOVING IN NEARLY THE OPPOSITE DIRECTION. THIS IS
LEADING TO THE FORMATION OF NEW SHOWER BANDS IN THE VICINITY OF THE
FRONTAL CONVERGENCE OVER THE AREA.
THE CHANGING ORIENTATION OF THE OLD FRONTAL BOUNDARY TO A MORE
EAST-WEST PATTERN AND THE INCREASING POSITIVE TILT OF THE TROPICAL
WAVE ADVANCING RAPIDLY AT LOWER LATITUDES HAS KEPT MODEL RUNS
GROPING FOR JUST THE RIGHT SOLUTION. EARLIER RUNS SHOWED VERY STRONG
RELATIVE HUMIDITY PEAKING FROM 00-06Z ON FRIDAY OVER THE
AREA...OSTENSIBLY FROM TROPICAL MOISTURE ARRIVING FROM THE
SOUTHWEST. LATER RUNS SHOW A BUCKLE IN THE FRONTAL BAND TONIGHT THAT
PULLS THE CONVERGENCE ZONE DOWN OVER AGUADILLA AND THEN RAPIDLY
RETREATS NORTH...AHEAD OF AN AREA OF SUBSIDENCE IN FRONT OF THE
TROPICAL WAVE. AS THE BAND OF MOISTURE ASSOCIATED WITH THE WAVE
BREAKS OFF FROM ITS TROPICAL SOURCE AND MOVES TOWARD THE NORTHWEST
INTO THE CONVERGENCE ZONE OVER THE AREA...THE BAND APPEARS TO SAG
SOUTH OVER SAINT CROIX LATE FRIDAY NIGHT TO MEET IT AND THEN
FLUCTUATE WILDLY BETWEEN 17 NORTH AND 23 NORTH ON SATURDAY...
POSSIBLY RESPONDING TO AFTERNOON CONVECTION OVER PUERTO RICO
SATURDAY AFTERNOON. EVEN THE WINDS ARE ERRATIC NEAR THE SHIFTING
BOUNDARY OF THE CONVERGENCE ZONE...VARYING FROM SOUTHEAST TO NEAR
CALM OVER THE NEXT SEVERAL DAYS IN THE 1000-850 MB LAYER.
YESTERDAY MODELS WERE SHOWING A LOW PRESSURE THAT BEGAN JUST EAST OF
THE YUCATAN PENINSULA AND TRAVELED NORTHEAST ACROSS HISPANIOLA AND
THEN INTO THE WESTERN ATLANTIC NORTH OF US...DEEPENING TO AS LOW AS
994 MB. TODAY THE LOW IS WEAKER AND LESS DISTINCT. IT IS DEPICTED AS
MOVING MORE SLOWLY UP FROM ITS SOURCE AREA. YESTERDAY IT WAS THE
REASON THAT THE FRONTAL BOUNDARY WAS TO MOVE OVER PUERTO RICO AND
THE U.S. VIRGIN ISLANDS MONDAY NIGHT. THE GFS NOW SHOWS THIS LOW
PUSHING THE BOUNDARY SOUTH OF US WEDNESDAY NIGHT NEXT WEEK. THE 15
TO 20 KNOT WINDS FORECAST FOR SUNDAY-MONDAY...AND NEVER QUITE
BELIEVED HERE...ARE NOW WEAKER AND LATER IN THE WEEK. A MORE LIKELY
SCENARIO IS THAT SMALLER AND WEAKER LOW PRESSURES WILL FORM IN AND
NEAR THE BOUNDARY AND CARRY OFF MOISTURE AND ENERGY TO OUR NORTHEAST
ALONG THE FRONT. IN RESPONSE...THE FRONT WILL GROW WEAKER AS TIME
PROGRESSES NEXT WEEK BUT WILL PROBABLY NOT MOVE AWAY FROM THE LOCAL
AREA...LEAVING US WITH GOOD CHANCES OF SHOWERS...ELEVATED RAINFALL
AMOUNTS AND MOSTLY CLOUDY WEATHER FOR ANOTHER 10 DAYS.
&&
.MARINE...THE MAIN HAZARD TO MARINERS IN THE UPCOMING 72 HOURS WILL
BE LIGHTNING FROM THE SCATTERED THUNDERSTORMS IN THE ATLANTIC AND
THE CARIBBEAN. SEAS ARE EXPECTED TO DROP TO 3 TO 4 FEET IN BOTH
WATERS AND WINDS WILL GENERALLY BE LIGHT TO MODERATE EXCEPT IN THE
IMMEDIATE VICINITY OF THUNDERSTORMS.
&&
.AVIATION...AREAS OF VERY POOR VISIBILITIES WILL CONTINUE IN THE
VICINITY OF THE FRONTAL BAND DUE TO THE HEAVY RAIN IN SHOWERS AND
THUNDERSTORMS BOTH OVER LAND AND SEA. TOPS ARE GENERALLY BELOW 30
THOUSAND FEET BUT ISOLATED TURRETS CAN REACH 45 THOUSAND. WHILE SOME
CLEAR LAYERS MAY BE FOUND BETWEEN LAYERS...THEY WILL BE PUNCTUATED
BY NUMEROUS CONVECTIVE TOWERS.
&&
.HYDROLOGY...ALTHOUGH HEAVY RAINS DID FALL...MAINLY IN THE EASTERN
PORTION OF PUERTO RICO...AND ALTHOUGH RAIN HAS FALLEN ALMOST
EVERYWHERE IN THE STATE...RIVERS HAVE RESPONDED ONLY WEAKLY TO THE
RAIN SO FAR. THE FLASH FLOOD WATCH WILL BE CONTINUED THROUGH THE
EVENING HOURS AT LEAST...IN ANTICIPATION OF MORE RAIN FORMING IN THE
CARIBBEAN AND MOVING ONSHORE OVER PUERTO RICO. ALTHOUGH RAIN HAS
FALLEN OVER SAINT THOMAS AND SAINT CROIX...AMOUNTS HAVE NOT BEEN
SUFFICIENT TO GENERATE FLOODING AND THIS IS EXPECTED TO REMAIN THE
CASE.
Looks like more wet weather for the caribbean but nothing that may develop into a tropical system but we will watch anyway.It's an enrichment pleasure to read that very long detailed discussion that let the people know what is going on in all levels of the atmosphere.
Broad low pressure still is shown at the 12z GFS but nothing of tropical in nature.
Last edited by
cycloneye on Thu May 12, 2005 3:58 pm, edited 1 time in total.
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