096 
FXCA62 TJSJ 060139
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
939 PM AST Tue Oct 5 2021

.UPDATE...Breezy conditions will continue across the region with
easterly trade winds between 15-20 knots. Passing showers will 
move from time to time across the U.S. Virgin Islands and over 
portions of Puerto Rico through the overnight hours and early 
morning hours. Winds will shift from the east to northeast on
Wednesday, and afternoon convection should develop mainly over the
Cordillera Central and southwestern quadrant of PR. Streamer type
of shower activity is also expected to develop downwind of the
USVI during the afternoon. Minor changes were made to the previous
forecast. 


&&

.AVIATION...Mainly VFR conditions are expected to prevail through
the forecast period. However, quick trade wind showers could move
at times across the USVI/Eastern PR terminals. The 06/00z TJSJ
sounding indicated east winds at 10-25 kt blo FL080. 


&&

.MARINE...No change from previous discussion. Small Craft Advisories
remain in effect through late Wednesday night, and a High Rip Current
Risk is in effect for the northern beaches of Puerto Rico,
Culebra, and the eastern beaches of St. Croix.


&&

.PREV DISCUSSION... /issued 525 PM AST Tue Oct 5 2021/ 

SYNOPSIS...

A ridging pattern aloft will hold until tomorrow. An increase in
moisture content due to remnants of Victor will aid in the 
development of showers and thunderstorms Thursday and Friday. Dust
concentration will remain low during the next several days. Choppy
to hazardous marine conditions will continue at least through
Wednesday.

SHORT TERM...Tonight through Thursday...

A mid and upper-level ridge will continue to hold over the area 
through tomorrow. Meanwhile, at lower levels, a surface high 
pressure north of the area will continue to promote brisk easterly
winds. PWAT values will remain near to below normal values for the
rest of the forecast period. Altogether, this will result in
relatively dry and stable conditions. However, the development of 
convective activity due to diurnal and local effects is expected 
each afternoon. Latest Aerosol Model guidance indicates that the 
dust concentration will remain low during the next several days.

For tonight, passing showers will continue across parts of 
eastern Puerto Rico and the local waters. This activity is
expected to continue through the early morning hours. This will be
followed by afternoon convection each day. Possible isolated 
thunderstorm activity and scattered to numerous showers will 
focus mainly over parts of interior and western Puerto Rico. Model
sounding suggest favorable winds to trigger streamer-like shower 
activity downwind from the U.S. Virgin Islands, Vieques and 
Culebra. Due to the fast steering flow, rainfall activity is not 
expected to be significant, therefore, the flooding potential is 
expected to remain low. The ridge aloft will weaken on Thursday, 
and the remnants of Victor will make its way towards the the 
forecast area. This will increase moisture content and will aid in
the development of deeper afternoon convection over interior and 
western Puerto Rico.

LONG TERM...Friday through Wednesday...

A typical weather pattern is expected through the end of the week. 
Therefore, isolated to scattered showers are expected every morning 
and during the night across the local waters, USVI, and eastern PR. 
Meanwhile, afternoon showers and isolated thunderstorms are expected 
mainly across the central and western sections of PR. However, 
things could get very rainy on Monday through Wednesday of next week 
if the model guidance were to verify as a tropical wave moves 
through.

A weak trough in the upper levels will prevail through the end of 
the week, but high pressure in the mid levels is expected to keep 
things fairly stable. This mid level high pressure, combined with 
precipitable water values below the normal, will limit the 
thunderstorm development to isolated areas in the afternoons. Better 
moisture advection is expected with precipitable water values near 
and above 2.0 inches starting late Monday and persisting through 
Wednesday of next week. The latest model guidance is also 
suggesting a broad coverage of shower activity across the local 
forecast area. We will closely monitor the potential for 
significant rain early next week, as this is still far in the
forecast period and confidence is low.

As far as temperatures, we can expect near normal highs and lows in 
the long term period. Highs in the upper 80s to near 90 across the 
lower elevations, with lows in the mid 70s to near 80. The higher 
elevations could observe highs and lows about 5 to 10 degrees cooler 
than the lower elevations, even slightly cooler in a few isolated 
areas. Heat index values will be near or slightly above 100
degrees across the lower elevations, especially from Thursday
through Sunday.

AVIATION...

Generally VFR conds expected across all terminals next 24 hrs. 
VCSH/brief SHRA are not expected to have operational impacts at 
terminals. Winds generally out of the east 10 to 15 knots, with 
stronger gusts and sea breeze variations. Only minor slowing of 
winds expected after sunset, to around 10 to 12 knots overnight. 
Winds increase again after sunrise.

MARINE...

Choppy to hazardous seas between 5 to 7 feet due to wind driven 
seas and a northeasterly swell are expected to continue across 
most of the regional waters through late Wednesday night. 
Therefore, there is a Small Craft Advisory in effect until late 
Wednesday night. There is a high risk of rip currents across the 
northern and eastern beaches of PR, Culebra and eastern beaches of
St. Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  80  88  78  90 /  40  40  40  30 
STT  78  90  79  89 /  40  40  30  40 

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Thursday afternoon for Culebra-
     North Central-Northeast-Northwest-San Juan and Vicinity-
     Southeast.

VI...High Rip Current Risk through Wednesday afternoon for St Croix.

AM...Small Craft Advisory until 8 AM AST Wednesday for Caribbean 
     Waters of Puerto Rico from 10 NM to 17N-Coastal Waters of 
     Southern USVI Vieques and Eastern Puerto Rico out 10 NM.

     Small Craft Advisory until 2 AM AST Thursday for Atlantic Waters 
     of Puerto Rico and USVI from 10 NM to 19.5N-Coastal Waters 
     of Northern Puerto Rico out 10 NM.

     Small Craft Advisory until 2 PM AST Wednesday for Anegada 
     Passage Southward to 17N-Coastal Waters of Northern USVI 
     and Culebra out 10 NM-Mona Passage Southward to 17N.

&&

$$

SHORT TERM...DSR
LONG TERM....ICP
PUBLIC DESK...FRG