Weather

491 
fxca62 tjsj 060118 
afdsju 


Area forecast discussion 
National Weather Service San Juan PR 
918 PM AST Monday Jan 5 2009 


Update... 
enhanced pop and weather grids to reflect the development of 
showers across the western interior of Puerto Rico. These 
showers...which developed thanks to low-level instability and 
moisture beneath a middle-level high...are expected to end by 
06/0200z. Otherwise...no other updates were made to the current 
forecast package. 


&& 


Aviation... 
mostly VFR conditions are expected to persist across all the 
local taf sites during the overnight hours and continuing through 
Tuesday morning. However...brief periods of MVFR conditions are 
possible across tkpk...and tncm from 0602/0612...due to scattered 
showers moving from time to time. Latest 06/00z sounding showed 
mainly east winds from the surface up to 10k feet. 


&& 


Previous discussion... /issued 352 PM AST Monday Jan 5 2009/ 


Synopsis...at upper levels...high pressure will build over the 
central Caribbean through Wednesday. The high will lean forward 
over Puerto Rico on Thursday and the Leeward Islands on Friday as a 
strong middle latitude trough pushes into the western Atlantic. High 
pressure remains entrenched over the southern Caribbean during the 
weekend and early next week and then rebuilds over Vieques and 
Culebra middle week. 


At middle levels...high pressure will build over the Greater Antilles 
during the week from its current position over the Yucatan 
Peninsula. The resulting ridge will persist through the beginning 
of next week. 


At lower levels...a ridge stretches from a 1026 mb high in the 
eastern Atlantic to Florida. The high will remain through the 
weekend but the ridge will drift southeast to Hispaniola and 
weaken ahead of a cold front that...although it never reaches the 
local area...will bring lighter winds and weaker gradients. High 
pressure rebuilds across the western Atlantic during the weekend. 
Easterly flow continues throughout the period. 


Discussion...it was another completely dry day except for a small 
streamer off the island of Saint Tomas that headed west northwest. 
Moisture remains limited and showers isolated or scattered across 
the area until Wednesday morning. Both the NAM and the GFS bring 
in a band of moisture that should dampen all of the Virgin Islands 
and eastern Puerto Rico by mid-morning...though the NAM is much 
more aggressive with this band. Wednesday has been evolving 
weather-wise in the models for the last 24 hours or so and it 
appears that they are now also delaying the dryer weather set for 
Wednesday night until Thursday afternoon. Otherwise...little 
change in the forecast and no significant precipitation events are 
foreseen in the next 10 days other than the scattered showers 
pattern seen thus far this year. 


Aviation...mostly VFR conditions are expected to persist across all 
the local taf sites for the rest of this afternoon and evening and 
continuing through Tuesday morning. However...the leading edge of a 
low level surge of moisture and showers could affect the U.S. Virgin 
Island airports during the overnight hours. That being said...expect 
briefly MVFR conditions across tist...tist...tisx...tncm and tkpk 
from late this evening through 0610z. Some mountain obscurations are 
expected for this period. 


Marine...seas continue to diminish over the area. The wave watch 
still indicates slightly higher seas in the Atlantic due to winds 
on Wednesday and then steadily decreasing seas until Saturday. At 
the moment no major events are foreseen in the next 7 days. 
Caribbean seas remain below small craft criteria throughout the 
period...highest seas due to wind waves on Wednesday and Sunday. 


&& 


Preliminary point temps/pops... 
sju 72 83 72 83 / 30 30 30 30 
stt 74 83 74 83 / 20 20 20 20 


&& 


Sju watches/warnings/advisories... 
PR...none. 
Vi...none. 
&& 


$$ 


71/02/ 

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