495 
fxca62 tjsj 220338 
afdsju 


Area forecast discussion 
National Weather Service San Juan PR 
1138 PM AST Friday Nov 21 2008 


Discussion...a dissipating frontal boundary to the northwest of 
Puerto Rico and an associated middle level vorticity off the northeast 
coast of Hispaniola...are expected to weaken over the remainder of 
the weekend...providing variable amounts of low level moisture to 
aid in some shower activity across Puerto Rico for the next 
couple of days. Models continue to indicate the trailing frontal 
boundary extending from the southern tip of Florida into the 
western Atlantic...will eventually reach the local Atlantic waters 
early next week...possibly crossing the islands on Tuesday or 
Wednesday. In addition...the low pressure system associated with 
this second frontal boundary is currently generating additional 
long period swell...which will likely reach the local waters early 
on Monday. However...short term focus remains on long period swell 
producing hazardous marine conditions across the local waters this 
evening. 


&& 


Aviation...VFR conditions to prevail across all of the local taf sites 
overnight. Limited shower activity expected Saturday over majority 
of the forecast area...with the exception of southwestern Puerto 
Rico (tjps and tjmz vicinities)...where MVFR ceilings/visibilities and mountain 
obscurations are possible from afternoon convection roughly 18z-22z. 


&& 


Marine...long period northerly swell Wills begin to diminish 
across the local Atlantic waters and Caribbean passages overnight 
and on Saturday. Buoy 41043 is continuing to indicate swells near 
8 feet at 11-13 seconds...which will easily produce large breaking 
waves of 10-15 feet advertised in the current high surf advisory. 
This advisory currently expires at noon Saturday. Additional long 
period swell being generated from a strong low pressure system 
across the western Atlantic will bring increasing seas and 
additional long period swell by early Monday morning. 


&& 


Previous discussion... /issued 552 PM AST Friday Nov 21 2008/ 


Synopsis...a cold frontal boundary extended from northeastern 
Hispaniola...east northeast across the local offshore Atlantic 
waters and then continued northeastward into the central Atlantic 
this afternoon. This old boundary will remain nearly stationary 
and weaken over the next few days...and then be reinforced by 
another cold front sinking into the local Atlantic waters Monday 
through Tuesday. High pressure forecast to build off of the 
southeastern U.S. And into the west and southwest Atlantic behind 
these two cold fronts will maintain a breezy wind conditions 
across the region into early next week. 


Discussion...the Doppler and satellite images are showing two 
areas of convection inside of our local forecast area. Scattered to 
numerous showers associated with a frontal boundary to the 
northwest of Puerto Rico could be seen over the offshore Atlantic 
waters. Another area of showers could be seen affecting the off shore 
Caribbean waters. Isolated to scattered showers developed over the 
west and southwest portions of Puerto Rico...with most of of these 
showers expected to dissipate around sunset. 


Winds are expected to shift slightly north tonight...this will 
increase the shower coverage across the northern coastal sections 
of Puerto Rico. 


A high surf advisory is in effect through noon Saturday. 


Aviation...mostly VFR conditions are expected across all of the 
local taf sites this evening. Only brief periods of MVFR conditions 
are expected after 00z this evening across tjsj and tjps...but in 
general no weather flying hazards are expected across the region 
during the next 24 hours. Latest tjsj 12z sounding indicated an east 
northeast wind flow up to 15 knots...from the surface to 10k 
feet...becoming southwesterly and then westerly and stronger above 
10k feet. 


Marine...large long period northwesterly swells will dominate the 
regional waters this afternoon and tonight...then become more northerly 
and slowly subside over the weekend. Another northwest swell will 
reach our local waters between Sunday and Monday generating once 
again dangerous conditions across the local waters. 


&& 


Preliminary point temps/pops... 
sju 73 85 74 84 / 40 50 50 50 
stt 75 85 75 85 / 30 30 20 30 


&& 


Sju watches/warnings/advisories... 
PR...high surf advisory until 12 PM AST Saturday for Culebra-Mayaguez 
and vicinity-north Central-Northeast-northwest-San Juan and 
vicinity-Vieques. 
Small Craft Advisory amz710-712-715-722-725-732-741-742-745. 


Vi...high surf advisory until 12 PM AST Saturday for St Croix- 
St. Thomas/St. John/adjacent islands. 
Small Craft Advisory amz710-715-722-725-732. 


&& 


$$ 


93/04/