Scientific Forecaster Discussion
fxca62 tjsj 242122
Area forecast discussion
National Weather Service San Juan PR
522 PM AST Fri Nov 24 2017
Synopsis...mid to upper level ridge will continue for the next
several days. Drier air and fair weather will persist through the
weekend. Overall moisture will increase by mid-week next week as
an induce trof moves over the area.
Short term...today through Sunday...showers and isolated
thunderstorms over western Puerto Rico are expected to diminish
during the evening hours. Ridge aloft and a drier air mass will
move over the region during the weekend. This will limit shower
activity across the islands. Therefore, mostly sunny to partly
cloudy skies will prevail with shallow afternoon convection over
sections of western PR during the afternoon hours. An east to
southeast wind flow will keep day time temperatures between the
high 80s to low 90s across the lower elevations. Overnight
temperatures will drop to the low 60s across the higher
Long term...from previous forecast...Monday through Saturday...
a patch of moisture develops just southeast of Puerto Rico and
moves onto the island during the day. Then ridging at 700 mb dries
the pattern out for another 12 to 24 hours. Then modest moisture
then prevails through the end of the work week. At upper levels
high pressure dominates the southern Caribbean and a deep polar
trough over the United States shears out and moves across the
Atlantic in a greatly weakened condition, passing just to the
north accompanied by an 65 knot jet late Wednesday. The trough
passage at upper levels will enhance shower activity somewhat with
good precipitable water values, but dynamics are weak. The jet
will hang just south of the area in northwest flow until it lifts
back across the area on Saturday. Patchy moisture Thursday through
Saturday will bring showers but mainly in the west and interior
portions of Puerto Rico.
Aviation...VFR conds...sct-bkn lyrs nr fl025...fl050 with vcsh
at most terminals til 24/23z. Few rain showers en Route btw islands and ovr
coastal waters. Few tops nr fl150. L/lvl wnds FM east-NE 10-15 kts blo
fl250...surface wnds mainly FM east 5-15 kts...except for local sea breeze
variations. No sig wx impacts at local terminals attm.
Marine...a 4-5 feet northeast swell is expected to reach the
local waters on Sunday. This will cause a moderate to high risk of
rip currents across the Atlantic beaches of the islands. Overall,
seas should continue between 3-5 feet across the offshore waters
and passages and at 4 feet or less across the nearshore waters of
the islands. East winds will continue between 5-15 knots.
Preliminary point temps/pops...
sju 88 77 87 77 / 40 40 40 10
stt 85 77 86 75 / 40 40 30 20
PR...Flash Flood Watch through Saturday afternoon for northwest-