218 
FXCA62 TJSJ 060900
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Mon Sep 6 2021

.SYNOPSIS...

A seasonal weather pattern will prevail early this week, with the
advection of patches of moisture from time to time and afternoon
convection enhanced by sea breeze variations. Warmer than normal
temperatures will persist across Puerto Rico and the U.S. Virgin
Islands. Hurricane Larry, located way off to the northeast over
the Atlantic Ocean, will produce a swell deteriorating marine and
coastal conditions tonight into mid-week.

&&

.SHORT TERM...Monday through Wednesday...

Mostly clear skies were seen across the local islands overnight. 
There were only a few showers over the local waters, with no 
measurable rain over land. Winds were generally light, at around 5 
mph out of the northeast. Minimum temperatures were in the mid 70s 
to near 80 in coastal areas and in the upper 60s to low 70s at 
higher elevations. 

A weakening TUTT low will continue to meander north of the local 
islands through Wednesday. At lower levels, as Hurricane Larry 
continues to lift towards the Central Atlantic, the steering winds 
will continue to prevail from the east northeast. The northeasterly 
wind flow will continue to drive the Saharan air layer away from the 
islands while simultaneously it is to enhance low level moisture 
convergence Tuesday and Wednesday. Nevertheless, precipitable water 
values over the region are expected to remain below normal today, at 
around 1.3 to 1.5 inches. Under this evolving pattern, continue to 
expect locally induced afternoon showers and thunderstorms across 
west areas of Puerto Rico each day as well as a higher incidence of 
early morning showers to affect the USVI and Atlantic coastal areas 
of Puerto Rico on Tuesday. Heat indices will again push into the 
100s with temperatures in many areas ranging from the upper 80s to 
lower 90s.

.LONG TERM...Thursday through Monday

Local weather will be tight at some degree to the final track of
Hurricane Larry. As Larry moves across the Atlantic Ocean (in a
safe position for PR/USVI), winds will be predominantly from the 
east to southeast through at least Saturday, resulting in a weak 
steering wind flow on Thursday. This weak steering wind flow will 
be allowing afternoon showers to last longer than usual, 
increasing the threat of flooding. However, the limiting factors 
seem to be below- normal available moisture. In addition, a 
Saharan Air Layer is forecast to arrive Thursday into Friday, 
promoting hazy skies.


A retrograding TUTT-Low moving over the Northeast Caribbean will 
induce surface perturbation on Saturday, increasing instability 
and convective activity Saturday and Sunday. Atmospheric 
conditions will remain favorable for the development of rain 
showers and thunderstorms with the arrival of a tropical wave 
Sunday afternoon, with its moisture lingering through Monday. 

&&

.AVIATION...

VFR conditions are expected at all TAF sites during the 
forecast cycle. Northeasterly winds at 10 to 15 knots with higher 
gusts and sea breeze variations aft 06/13z.

&&

.MARINE...

Hurricane Larry, which is moving across the Atlantic Ocean far to
the northeast, will deteriorate the Atlantic Waters marine
conditions through mid-week. Larry's swell will increase seas
between 6 and 8 feet across the Offshore Atlantic waters and the
Anegada Passage throughout the day. Small Craft Advisories are in
effect for these waters. Then, as additional swell energy arrives
Tuesday and Wednesday, hazardous seas will spread into the coastal
Atlantic waters of PR and the U.S. Virgin Islands, causing
dangerous coastal conditions. Marine conditions are forecast to
improve around Thursday night or early Friday.

Beachgoers, Cramer Park has a high risk of rip currents.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  90  80  90  80 /  20  50  50  30 
STT  91  79  89  79 /  20  50  50  30 

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...VI...High Rip Current Risk through Wednesday afternoon for St Croix.

AM...Small Craft Advisory from 2 PM this afternoon to 2 PM AST 
     Tuesday for Anegada Passage Southward to 17N-Coastal Waters 
     of Northern USVI and Culebra out 10 NM-Coastal Waters of 
     Southern USVI Vieques and Eastern Puerto Rico out 10 NM.

     Small Craft Advisory from 8 AM this morning to 2 AM AST Thursday 
     for Atlantic Waters of Puerto Rico and USVI from 10 NM to 
     19.5N.

&&

$$

SHORT TERM...OM
LONG TERM....CAM
FIRE WEATHER...TW