210
FXCA62 TJSJ 070846
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
446 AM AST Tue May 7 2024

.SYNOPSIS...

A wet and unstable weather pattern will continue across the
islands through at least mid-week due to an approaching mid- to
upper-level trough and abundant tropical moisture. The risk of
flooding will be elevated to locally significant due to already
saturated soil and much above-normal river levels. Temperature-
wise, due to the high moisture content, places without rain
activity may experience above-normal heat indices (thus apparent
temperatures) that surpass 100 degrees Fahrenheit.

Pulses of northeasterly swells propagating across the Atlantic
Ocean will arrive later tonight through the weekend, likely
causing life-threatening rip currents along the northand east-
facing beaches in PR and the USVI.

&&

.SHORT TERM...Today through Thursday...

During the overnight hours, calm conditions have persisted over
most of the islands, however, showers have continued over local
waters. Some of those showers moved inland, especially over
eastern PR, Vieques, and San Juan vicinity, leaving approximately
1.0 to 1.5 inches of additional rain. Flood warnings remain in
effect along the Rio Cibuco, Rio Grande de Manati, and Rio
Guanajibo. We urge citizens to stay informed and not cross flooded
roads.

The forecast remains on track during the short-term period. A
wetter and more unstable pattern will persist with an elevated to
significant risk of flooding through midweek. Plenty of moisture
will remain present today and Wednesday with above than normal
values of precipitable water (around 2.0 to 2.4 inches). Based on
the latest weather models, high pressure over the western Atlantic
will maintain light to moderate easterly to northeasterly winds at
the surface. On the other hand, an upper-level trough will continue
to swing by our region through mid-week, keeping favorable
conditions aloft for the wet and unstable pattern to prevail this
afternoon into Wednesday. In addition, mid-level temperatures will
drop to around -8 degrees Celsius tonight enhancing the potential
for thunderstorm development.

Please note that due to already saturated soils and much above
normal river streamflows, any brief period of moderate to locally
heavy rain or persistent light rainfall could lead to dangerous
flooding problems, as well as sudden mudslides and landslides in
areas of steep terrain. For that reason, we encourage residents and
visitors to remain weather-aware and informed about these potential
hazards. Be alert for any possible issuance of flood products.

During tonight`s period, expect a similar scenario in comparison
with last night, where shower and isolated thunderstorm activity
shift to the local waters and coastal areas of northern and eastern
Puerto Rico, Vieques, Culebra, and the U.S. Virgin Islands. By
Thursday, improving weather conditions are expected to develop as
the mid to upper-level trough moves away and a mid-to-upper-level
ridge builds and dominates across the region. Moisture levels should
drop to near-normal levels, resulting in a more stable atmosphere
and hopefully a break from the current conditions. Any afternoon
convection that could develop will be due to local effects and sea
breeze variations.

Temperature-wise, hot and humid conditions will prevail throughout
the period. Daytime highs in the upper 80s to low 90s along the
coastal/urban areas and lows in the upper 70s to low 80s along the
higher terrains. Combined with above-than-normal moisture, heat
indices may reach 100F or higher across coastal areas of Puerto
Rico as well as the rest of the islands through the period.

.LONG TERM...Friday through Tuesday

Model guidance suggests a mid- to upper-level ridge is trying to
build over the Northeast Caribbean Friday into the weekend,
promoting stable conditions and potentially bringing relief from
the current weather conditions.

Once again, GFS Total Precipitable Water guidance suggests
returning the climatological values for this time of year, with
the advection of occasional patches of increased moisture.
Combining high moisture content with the typical upper 80s to low
90s maximum air temperatures will result in heat indices between
100-107 Fahrenheit or even higher, especially during the daily
maximum heating, across the USVI and PR`s urban and coastal areas
where no significant rain is observed.

Although we expect variable weather conditions with a mixture of
sunshine/clear skies and clouds each day, local effects and sea
breeze fluctuations may promote strong afternoon convection each
day. Furthermore, the advection of a cooler air mass across the
above-normal warmer sea surface temperature may result in frequent
nighttime showers, affecting the windward sections and local
waters each night.

The NASA aerosol optical thickness (AOT) guidance suggests the
arrival of an air mass with possible African Dust Particles by the
upcoming weekend, which may extend into next week.

&&

.AVIATION...
(06Z TAFS)

Mostly VFR conditions expected this morning but VCSH should continue
near TJSJ and USVI sites. The potential for VCTS and showers are
expected to increase during the afternoon across all sites.
VCTS/TSRA may continue to promote tempo MVFR to brief IFR conditions
later today. Higher winds and reduced vis near thunderstorms. E
to NE surface winds at 10-15 kts, and then becoming lighter and
more variable at night.

&&

.MARINE...

The surface high-pressure building north of the islands from the
Western to Central Atlantic will maintain a shearline south of the
islands across the Northeast Caribbean, promoting light to
moderate trade winds. Pulses of northeasterly swell will spread
across the regional waters later tonight onward. Unsettled weather
conditions due to strong thunderstorms are likely (especially
during the afternoon and evening) today and tomorrow.

&&

.BEACH FORECAST...

Expect increasing seas of 3 to 4 feet across most of the local
beaches in the Atlantic, mainly from the northeast, at 6 to 8
seconds. Across the Caribbean, seas will range around 2 feet from
the east to southeast at 6 to 8 seconds. Therefore, we expect the
risk of rip currents to increase to moderate today.

Pulses of northeast swells, with wave periods of 10 to 13 seconds,
will increase the risk of rip currents to moderate from late
tonight into next weekend across the north and east-facing beaches
of PR and the USVI. There is still a possibility of a high risk of
rip currents during that period; it`s crucial to monitor the beach
forecast for possible updates to the expected conditions as the
coastal hazards can change rapidly.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM/AVIATION...YZR
Synopsis/LONG TERM/MARINE/BEACH FORECAST....CAM