Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 190025
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
825 PM AST Sat Nov 18 2017

.UPDATE...Numerous showers and thunderstorms developed
this afternoon and evening mostly along and north of Cordillera
Central of Puerto Rico. Several Flood Advisories and a Flash Flood
Warning were issued for numerous municipalities along and north of
Cordillera Central of Puerto Rico as well as for the U.S. Virgin
Islands. This activity was associated with moisture provided by a
frontal boundary to the west and north of the region. An unsettled
and rainy weather pattern is expected to continue tonight and on
Sunday as the frontal boundary remains close to the region,
keeping the local islands under higher than normal moisture.
Cloudy skies and periods of showers and possible isolated
thunderstorms are forecast through the rest of the weekend and
early next week. Urban and small stream flooding and flash flood
warning are possible especially on Sunday afternoon.

&&

.AVIATION...SHRA/TSRA expected to continue across the local area
tonight, causing VCSH/VCTS across the local terminals with TEMPO
MVFR conds possible at TJBQ, TJSJ as well as across the USVI TAF sites.
CIGS will be mainly above FL120 before 19/14Z. CIGS are expected
at FL050 and at times close to FL030 with SHRA/TSRA after 19/16Z.
Winds will be mainly southwesterly overnight generally at 10kt or
less.

&&

.MARINE...Not changes to previous reasoning

&&

.PREV DISCUSSION... /issued 816 PM AST Sat Nov 18 2017/

SYNOPSIS...
A weak frontal boundary is causing showers and thunderstorms
across Puerto Rico and the U.S. Virgin Islands. The heaviest rain
is currently over the St. Thomas and the U.S Virgin Islands, but
doppler Radar and satellite imagery is showing deep convection
beginning to form over the central interior and northeast Puerto
Rico. Mostly cloudy conditions helped keep wide spread convection
from firing early today due to surface heating being limited
during the morning and afternoon. Otherwise, deep tropical
moisture will continue to be drawn over the forecast area through
Sunday thus causing showers and thunderstorms.

SHORT TERM...Tonight thru Monday
A front that has bought unsettled weather to Puerto Rico and the
U.S. Virgin Islands remains to the west of the island. This front
is pulling moist tropical air across the region and causing
showers and thunderstorms. Over the next several hours the
strongest showers and thunderstorms will be over the interior,
northeast, Vieques, St. Thomas and st. Croix, but other areas
could see showers develop.The combination of a weak frontal
boundary, an induced surface trough, a southerly wind flow and
good ventilation aloft will help in the development of showers and
thunderstorms through Sunday. The only limiting factor at this
time is cloud cover not allowing enough heating at the surface to
trigger showers and thunderstorms Sunday.

LONG TERM...Tuesday through Sunday...(Previous Discussion)
As a mid to upper level ridge strengthens across the forecast
area early the next work week, available moisture will quickly
erode with precipitable water values remaining near the normal
range through the forecast period. Under the ridge aloft and
easterly winds bringing those patches of low level moisture at
times, expect mainly fair and stable weather condition much of the
next work week with trade wind showers across USVI and E PR as
well as some locally induced afternoon showers across west areas
of Puerto Rico each day. Seasonable temperatures are also expected
as easterly winds will return to the area.

AVIATION...
SHRA/TSRA will continue across the Flying area through the
overnight hours. VCSH/VCTS across the local terminals with TEMPO
MVFR conds at TJSJ/TIST/TJPS/TISX/TJBQ til 18/22z. BKN/OVC are
likely and will be mainly above FL050 but in/near SHRA/TSRA could
be near FL030. In addition with this activity expect VIS around
4SM. SFC winds from the SW btwn 6-12 kt but gusty and VRB near
TSRA, then light to calm and VRB aft 18/23z.

MARINE...Seas 3 to 5 feet with occasionally seas up to 6 feet are
expected across the Atlantic waters due to small northerly swell.
Elsewhere seas of 2 to 4 feet. Wind direction will vary over the
local waters but generally at 10 knots or less. A moderate risk
of rip currents is expected across the north beaches of Puerto
Rico and Culebra.

$$

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  78  86  77  86 /  50  50  30  30
STT  78  86  78  85 /  40  40  40  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Flash Flood Watch through Sunday afternoon for Northwest-Western
     Interior.

VI...None.
AM...None.
&&

$$

SHORT TERM...JF
LONG TERM....TW



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