Area Forecast Discussion
Issued by NWS San Juan, PR

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874
FXCA62 TJSJ 150121
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
921 PM AST Fri Dec 14 2018

.UPDATE...
Tonight`s shower activity was due to the combination of breezy
trade winds and a surge of low-level moisture which brought fast
moving showers across portions of the islands. Satellite and radar
imageries detected a slot of dry air which will filter from the
east across the islands overnight.

Strong surface high pressure drifting from the west to central
Atlantic will result in breezy conditions across the area through
at least the upcoming week. Mid-upper level ridge will hold aloft.
As a result, patches of low-level moisture will move periodically
across the region, producing a mixture of sunshine/clear skies
and clouds with occasional trade wind showers each day.

&&

.AVIATION...
Quit weather conditions will prevailed overnight, but passing
SHRA/-SHRA can not be ruled out at TJSJ/TIST/TISX/TNCM/TKPK at
times through the forecast period. Calm to light and variable
winds are expected at TJPS/TJMZ, but easterly winds around 10
knots with occasional gusts are expected elsewhere overnight.
Easterly winds will increase at 15 to 20 knots with higher gusts
after 15/13z.

&&

.MARINE...Rough seas up to 7 feet are expected across most of the
regional waters. Seas will increase around 8 feet during the
weekend. Therefore, small craft advisories are in effect.

The risk of rip currents is forecast to turn high for the north
and east facing beaches of Puerto Rico and the U.S. Virgin
Islands tomorrow.

&&

.PREV DISCUSSION... /issued 520 PM AST Fri Dec 14 2018/

SYNOPSIS...Surface high pressure across the Atlantic will move
east, tightening the pressure gradient this weekend. Surface low
to strengthen across the western Atlantic on Monday, weakening
the local winds. Mid and high level ridges to prevail for the next
few days, causing a stable atmosphere. Patches of moisture will
bring bring showers through the weekend.

SHORT TERM...Tonight through Sunday...

Surface high pressure north of the local area is tightening the
local pressure gradient, causing breezy conditions. Patches of
moisture will bring some showers to the local area but these
should be of short duration. This pattern will continue through
the weekend since we have a mid and upper level ridges which will
keep a stable atmosphere. Forecast soundings show a strong
inversion through the weekend, which indicates that the showers
expected will continue to be brief and shallow, deep convection is
not expected. Bottom line is that this weekend we expect breezy
days with near normal temperatures, mix of sun and clouds with
isolated to scattered brief showers.

LONG TERM...Monday through Saturday...

..From previous discussion...

A strong ridge of high pressure is forecast to hold northwest of
Puerto Rico through the extended period. The ridge will generate
trade wind showers over the area with easterly winds ranging from
15 to 20 mph. On Tuesday the GFS shows a weak jet stream moving
through Puerto Rico, then the ridge is expected to strengthen over
the region again. The middle to upper levels of the atmosphere
will remain devoid of significant moisture, thus only scattered
showers are forecast mainly over portions of northern, eastern,
interior areas of Puerto Rico, and the U.S. Virgin islands.
Showers that develop will be brief and only produce light rainfall
amounts. Otherwise stable weather is forecast through the long-
term period with an occasional passing shower.

AVIATION...VFR except for passing low level clds and OCNL SHRA ovr
regional waters and en route btw islands. Wnds fm E 20-25 kts BLO
FL250. Sfc wnds fm E 15-20 kts w/ocnl hir gusts bcmg 10 kts or less
aft 14/22z. SCT Ocnl BKN lyrs nr FL025...FL040...FL080 durg prd.
No sig wx impacts attm.

MARINE...High risk of rip currents continue across the northern
beaches of PR and Culebra, now also for Cramer Park in Saint
Croix. As the winds continue to increase and seas deteriorate
further, northwestern Saint Thomas will have a high risk of rip
currents as well. Northerly swell to invade the local waters
through the weekend, deteriorating the local seas in combination
of increasing seas. Small craft advisory in effect for most of the
local waters for seas up to 7 feet tonight, increasing up to 8
feet by Saturday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  76  84  75  84 /  50  50  50  50
STT  76  82  75  81 /  50  50  50  50

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through late Saturday night for Culebra-
     North Central-Northeast-San Juan and Vicinity.

VI...High Rip Current Risk through late Saturday night for St Croix.

     High Rip Current Risk from 6 AM AST Saturday through late
     Saturday night for St.Thomas...St. John...and Adjacent
     Islands.

AM...Small Craft Advisory until 2 AM AST Monday for Anegada Passage
     Southward to 17N-Caribbean Waters of Puerto Rico from 10 NM
     to 17N-Coastal Waters of Northern Puerto Rico out 10 NM-
     Coastal Waters of Northern USVI and Culebra out 10 NM-
     Coastal Waters of Southern USVI Vieques and Eastern Puerto
     Rico out 10 NM-Mona Passage Southward to 17N.

     Small Craft Advisory until 2 PM AST Monday for Atlantic Waters
     of Puerto Rico and USVI from 10 NM to 19.5N.

&&

$$

UPDATE...CAM
AVIATION...CAM



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