Area Forecast Discussion
Issued by NWS San Juan, PR

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

FXCA62 TJSJ 070834

Area Forecast Discussion
National Weather Service San Juan PR
434 AM AST Sun Aug 7 2022

A tropical wave will continue to move across the area today,
bringing an increase in shower and thunderstorm activity to the
area, along with gusty winds. Drier weather is expected for the
beginning of the workweek, along with some Saharan dust.


.SHORT TERM...Today through Tuesday...

Satellite and radar images indicate the arrival of the leading edge
of the next tropical wave already moving through the region.
According to GOES-16 Total Precipitable Water, moisture values
​​are about 1.7 inches over the islands, with the bulk of the
moisture over the Caribbean waters with values around 2.1 inches.
As the day progresses, the axis of the wave is expected to move
closer to the region, gradually increasing the potential for
shower and thunderstorm activity. This activity will bring gusty
winds, especially with the heaviest showers for portions of the
eastern third of Puerto Rico, the US Virgin Islands, and along the
local waters. In addition, diurnal-induced convective activity
will affect sections of the interior and western Puerto Rico this
afternoon into the early evening hours.

As the moisture from the previous tropical wave moves out of the
region, a drier trend is forecast to begin late Monday in the
afternoon through Tuesday afternoon as a drier air mass with
Saharan Dust particles filters into the region. According to the
NASA Goddard Earth Observing System Model, the bulk of the Saharan
particles will be on Monday. Although weather conditions will not
be conducive for widespread shower activity, afternoon convection
will still be possible, mainly focusing on western sections of
Puerto Rico, and less activity expected for the eastern areas.
Temperatures should remain typical for the season with highs in
the low 90s and heat indexes in the low 100s. By Tuesday, the
frequency of showers is forecast to increase as a a wind surge
drags another patch of enhanced moisture.

.LONG TERM...Wednesday through Sunday...
A mid to upper level ridge continues to hold northeast of the local
islands. Due to the anticyclonic flow created by the upper level
high, winds at these levels will be from the south, with moisture
being dragged from the Caribbean Sea that could aid in the
development of high clouds. At the mid-levels, dry air will dominate
through the end of the workweek. On Wednesday, however, a modest
increase in showers is expected as a tropical wave moves south of
the islands. There is some Saharan dust embedded within the
airmass that may result in hazy skies. Even with the limiting
factor of the dry air in the mid-levels, afternoon convection is
still expected to develop across western Puerto Rico due to local
effects. Additionally, occasional patches of moisture dragged by
the trade winds may bring some passing showers for eastern Puerto
Rico and the Virgin Islands. By the end of the workweek, while the
mid-dry air layer remains, the upper level ridge collapses in
response to an upper level trough north of the Bahamas, which
could promote better conditions aloft for thunderstorm

For the weekend, uncertainty increases in the forecast. First of
all, the GFS shows a tropical wave crossing the area on Saturday,
which could increase the potential for some showers. However, the
ECMWF shows the continuation of generally dry air covering the
northeastern Caribbean. The global models due agree in the formation
of a tropical cyclone that should remain north of the local islands.
Based on the current guidance, the main weather impacts will be a
weaker low level wind flow. However, the bulk of the moisture
associated with this system should remain far away from the
islands. Since this a long-term forecast, the users should pay
attention to the progress of this system as adjustments could be
introduced later in the week.


.AVIATION...VFR conditions are expected across most of the TAF
sites. A tropical wave moving to the area will result in SHRA and
VCTS for TIST, TISX, TJSJ, and TJBQ, causing some briefly MVFR
conditions with the heaviest activity. Low-level winds winds are
from the E at 10 kts with some gusty wind, increasing at 07/14Z up
to 15 to 20 KT, with seas breeze and some higher gusty winds. Some
VCTS are possibles across TJPS in the late afternoon hours.


Increasing winds will create choppy to hazardous seas today along
the Anegada Passage and the Atlantic waters through the day, with
seas rising up to 7 feet. Winds of 20 to 25 knots are also
anticipated for the Atlantic coastal waters north of Puerto Rico.
As a tropical wave moves trough, squally weather is also
anticipated for the local waters.

For the beaches, there is a high rip current risk for the northern
coast of Puerto Rico, Culebra and St. Croix.


SJU  90  78  90  78 /  50  50  40  40
STT  91  79  90  78 /  60  30  20  20


PR...High Rip Current Risk through Monday morning for Culebra-North
     Central-Northeast-Northwest-San Juan and Vicinity-Southeast.

VI...High Rip Current Risk through Monday morning for St Croix.

AM...Small Craft Advisory until 2 PM AST this afternoon for Anegada
     Passage Southward to 17N.

     Small Craft Advisory from 11 AM this morning to 8 PM AST this
     evening for Coastal Waters of Northern Puerto Rico out 10

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



LONG TERM....ERG is the U.S. government's official web portal to all federal, state and local government web resources and services.