596 
FXCA62 TJSJ 151606 AAA
AFDSJU

Area Forecast Discussion...UPDATED
National Weather Service San Juan PR
1206 PM AST Sun Nov 15 2020

.UPDATE...Showers are moving through the inner waters at the
moment, but will not likely last long or leave significant 
accumulations. Sounding again showed a very dry atmosphere above
10 thousand feet and was capped at 12-15 thousand feet making
anything except shallow isolated and local convection nearly
impossible. Minor changes to POPs and temperatures released with
full package update.

&&

.AVIATION...VFR conds will prevail at all TAF sites next 24 hours.
Sct SHRA to dvlp SW PR for a few hrs aft 15/17Z. Sfc winds 10-15
kt with gusts to 23kt psbl. Winds bcmg less than 12 kt aft 15/22Z. 

&&

.MARINE...Little change in overall situation, but minor increases
in wave action have added a high risk of rip currents to the rest
of today and tonight for northwest and the north central Puerto
Rico beaches. Small craft advisory conditions still expected on
Friday for the outer Atlantic waters and the northern part of the
Anegada Passage. Maximum winds NNE 30-40 kt btwn FL190-360 and NW
30-35 kt btwn FL430-470.

&&

.PREV DISCUSSION... /issued 443 AM AST Sun Nov 15 2020/ 

SYNOPSIS...The local islands will be in the subsident side of an
upper low to the east northeast today and early Monday, but a 
broad trough starts approaching the local islands from the 
northwest by midweek. A tropical wave is expected late on Tuesday 
into Wednesday, and available moisture will increase through from 
that point through the end of the week. Relatively benign weather 
is expected today, with only isolated to scattered brief showers, 
as northeast winds with drier than normal available moisture is 
expected.

SHORT TERM...Today through Tuesday...

The islands will remain under the envelop of a drier air mass 
through the day. However, the latest imagery from Total Precipitable 
Water shows a pocket of slightly higher values north of the area, 
resulting in some passing showers that may move over northern and 
eastern Puerto Rico and the U.S. Virgin Islands early in the day. 
The main feature over the area is a mid to upper level low pressure 
just to the east of the Lesser Antilles. Since the forecast area 
remains in the subsident side of this system, conditions are 
expected to remain unfavorable for strong convection to develop. 
In the afternoon however, local effects should combine with low 
level moisture to generate showers over southwestern Puerto Rico.

For tomorrow, the local guidance indicate that the mid-level low 
will move closer to the regional area, which should weaken the trade-
wind inversion. Additionally, a little bit more moisture is expected 
to filter in. As a result, morning showers will continue to be 
advected over eastern PR/USVI early in the day, followed by more 
showers over the interior and western Puerto Rico. For Tuesday, a 
tropical wave will also provide approach the local islands. Also, 
both the GFS and ECMWF models are indicating mid-level temperatures 
cooling down to around -6 degree Celsius. Due to this increase in 
instability, there will be the potential for some afternoon 
thunderstorms developing over western Puerto Rico. Some ponding of 
water on low-lying and poor drainage areas will be possible with 
this activity. 

LONG TERM...Wednesday through Monday...

The latest guidance has backed off compared to yesterday, and now
indicates less amount of rain, but still a similar pattern to 
what it was previously forecast. That said, a rainy or perhaps 
unsettled pattern is forecast this upcoming workweek, especially 
starting late Tuesday into Wednesday and onward, as a tropical 
wave approaches the local area, causing a significant increase in 
available moisture. In addition to the tropical wave, the latest
model guidance still indicates that a SFC low pressure across the
western Atlantic will move north and make way for a surface high 
pressure to enter the western Atlantic, which then causes the 
frontal boundary to stall to our north and keep the local islands
under the deep moisture through at least Saturday, with some faint
indication of drier air moving in on Sunday and Monday. It appears
now that Wednesday and then Friday would be the rainiest days in 
the long term forecast, with Friday being the rainiest as a
shortwave trough moves through. This sort of inconsistency in the
model increases uncertainty and one must also consider that the
model develops yet another tropical system in the southwestern
Caribbean, which may have an impact in the model solution for the
local area depending on its intensity and track.

AVIATION...VFR conds expected across all terminals through the 
forecast period. VCSH could develop after 15/17Z across TJPS, 
which could result in brief MVFR conditions due to reduced 
visibility and lower ceilings. Winds will be out of the northeast 
at 10 to 15 knots.eriod. VCSH could develop after 15/17Z across 
TJPS, which could result in brief MVFR conditions due to reduced 
visibility and lower ceilings. Winds will be out of the northeast 
at 10 to 15 knots.

MARINE...East to NE winds up to 15 knots today will cause choppy
seas up to 6 feet across the local waters. Therefore small craft 
operators are urged to exercise caution. These moderate winds will
continue for the next few days, causing seas to be generally
between 3 and 6 feet. There is a moderate or low risk of rip
currents across the local beaches for the next several days.
A northerly swell is possible late this week, which may cause 
seas to become hazardous.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  86  75  87  76 /  40  50  50  30 
STT  87  75  86  76 /  20  30  30  30 

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through late tonight for North Central-
     Northwest.

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

$$

SHORT TERM...WS
LONG TERM....CVB
PUBLIC DESK...GL