727
FXCA62 TJSJ 130900
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Sat Jul 13 2024

.SYNOPSIS...

A tropical wave and its moisture field will move across the
region leading to an increase in showers and thunderstorms
throughout the weekend. To start the next workweek, a TUTT will
approach the region enhancing instability and maintaining the wet
and unstable pattern in place through at least the first part of
the next workweek. An elevated heat risk as well as saharan dust
particulates will persist. A Small Craft Advisory is in effect for
the offshore Atlantic Waters, through this afternoon, and for the
Anegada Passage, through noon. Small Craft should still exercise
caution over most of the other local waters.

&&

.SHORT TERM...Today through Monday...

A tropical wave and associated moisture field will continue to cross
the Lesser Antilles bringing an increase in showers and thunderstorm
activity across the region through the weekend. By Monday, a TUTT is
still forecast to cross the region from the east. This will enhance
instability and thus maintain a moist and unstable pattern through
the forecast period. Another extensive plume of Saharan dust will
trail the aforementioned tropical wave with elevated heat risk
likely to persist during the period.

Skies were partly cloudy to variably cloudy overnight with scattered
passing showers and isolated thunderstorms noted over the coastal
waters and local passages. Showers and thunderstorms continued to
quickly reach parts of the north and east coastal areas of the
islands, producing periods of moderate to locally heavy downpours and
brief gusty winds. Overnight low temperatures were in the upper 70s
to near 80 degrees along the coastal areas and in the upper 60s to
low 70s in higher elevations and valleys. Surface winds generally
from the east 5 to 10 mph.

For the rest of the day, the presence of Saharan dust along with the
increasing moisture and a mix of sunshine and clouds will aid in
maintaining hazy conditions in some areas. However, the potential
for shower and thunderstorm development will continue to increase
during the afternoon and into the evening hours as the tropical wave
approaches the region. Although convective development will not be
continuous over the islands, periods of enhanced afternoon
convection will be likely across the islands and coastal waters.
This in turn will lead to periods of locally heavy rains and moderate
to high potential for urban and small stream flooding in isolated
areas as well as rapid increase in water level and surges along
rivers and small streams.

For the rest of the period, lingering suspended Saharan dust
particulates is expected to continue across the region. This
along with trailing moisture from the tropical wave and the
presence of a retrograding Tutt will maintain unstable conditions
enhanced by the good heating each day. As a result, isolated but
strong afternoon convection will remain likely especially across
the central and west to northwest sections of Puerto Rico.

.LONG TERM...Tuesday through Friday...

Humid and unstable conditions will be present to start the period.
A TUTT low will be north of our region on Tuesday while persistent
remnant moisture from the tropical wave from the short term period
will continue to push precipitable water (PWAT) values to above
normal, between 2.0 and 2.2 inches. At surface level, a high
pressure across the Atlantic will persist and promote light east to
east-southeast winds on Tuesday. Winds will increase, becoming
breezy, by the second half of the workweek. Patches of above normal
moisture will continue reaching the islands through midweek. The
TUTT low will move away from the region by Wednesday. Although some
saharan dust will linger, a more noticeable plume will approach the
islands by the second half of the workweek. More normal PWAT values
will be seen on Thursday. Current model guidance suggests another
upper low will approach the area on Friday, increasing instability.
Moisture will also gradually increase on Friday as a another
tropical wave and associated moisture move into the islands to end
the long term period. For Thursday, more typical weather with
passing showers in the morning and afternoon convection steered by
east to east-southeast winds. The other days in the period will have
more wet and unsettled weather due to the aforementioned features
and/or available tropical moisture. Warm conditions are still
expected for most of the period. Highs will be in the upper 80s to
around the low 90s in lower elevations of the islands. With
available moisture and east to east-southeast winds, heat indices in
coastal, urban and lower elevation areas can reach above 108 degrees
Fahrenheit.

&&

.AVIATION...

(06Z TAFS)

A tropical wave now crossing the Lesser Antilles will bring SCT
SHRA/ Isold TSRA across the area promoting brief MVFR/psbl IFR at
TIST/TISX/TJSJ with MTN Top Obscr psbl eastern Cordillera Central
til 113/14Z. Slight HZ will linger due to suspended Saharan dust,
but flight VIS should be plus 6SM. SHRA/VCTS ovr regional waters
and en route btw islands. SFC wnd will be fm the ENE btw 5 to 10
kts bcmg more easterly 12-15 kts with higher gusts and sea breeze
variations aft 13/14Z. Stronger gust likely w/Isold TSRA.

&&

.MARINE...

A surface high pressure across the Atlantic Ocean will promote
moderate to fresh easterly to east southeasterly winds through
tonight. Seas up to 7 feet are expected today across the offshore
Atlantic Waters and Anegada Passage. A tropical wave and associated
moisture field and wind surge will promote an increase in showers and
thunderstorm activity across the waters. The axis of the wave will
cross the region today, promoting unsettled weather conditions
throughout the weekend with its residual moisture. A TUTT will
approach the region to start the next workweek maintaining a moist
and unstable pattern.

&&

.BEACH FORECAST...

There is a moderate risk of rip currents for most beaches in Puerto
Rico, Vieques, Culebra, and the U.S. Virgin Islands. The risk
will start decreasing for several areas tonight through tomorrow.
For more details, please refer to the Surf Zone Forecast
(SRFSJU).

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...Small Craft Advisory until 6 PM AST this evening for AMZ711.

     Small Craft Advisory until noon AST today for AMZ723.

&&

$$

SHORT TERM...RAM
LONG TERM....MRR