743
FXCA62 TJSJ 060802
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
402 AM AST Mon May 6 2024

.SYNOPSIS...

A surface high-pressure building across the Western Atlantic will
promote the pooling of above-normal moisture content across the
Northeast Caribbean through at least mid-week. A trough between
the mid and upper levels will swing by late tonight through
Thursday, enhancing the dynamic aloft. Due to the soil saturation
across the islands and the much above-normal streamflows along
PR`s principal rivers, afternoon and evening convection may result
in sudden urban and small stream flooding each day. Additionally,
due to the high moisture content, places without no rain may
experience above-normal heat indices (thus apparent temperatures)
surpassing 100 degrees Fahrenheit.

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

&&

.SHORT TERM...Today through Wednesday...

Last night, showers developed mostly in north-central Puerto Rico
resulting in several Flood Advisories for municipalities in that
area. Radar estimates recorded around 2 to 3 inches of rain in
municipalities such as Arecibo, Barceloneta, Manati, Vega Baja, and
Toa Alta, among others. Approximately, up to 5 inches of rain fell
on northern coastal waters. Later, additional showers developed over
the eastern sector of Puerto Rico leaving between 1 to 2 inches of
rain. During the overnight period, calmer weather conditions
dominated across most of the island and the USVI, while showers
continued over Atlantic waters and eastern PR. Minimum temperatures
have been in the mid and upper 70s across most coastal sites and in
the mid and upper 60s along mountains and valleys.

The wet pattern will persist during this period. Plenty of moisture
will remain present over the next couple of days with above than
normal values of precipitable water (around 2.0 to 2.4 inches).
Based on the latest weather models, a high pressure establishing
over the western Atlantic will maintain light to moderate winds
mainly from the east at the surface, while an upper-level trough
will move through mid-week keeping wet and unstable conditions
continuing across our region. For today, the National Blend of
Models (NBM) suggests some shower activity could begin earlier
across eastern sectors of Puerto Rico, and then concentrate over the
interior and west central areas later. During the afternoons from
today through midweek, showers and isolated thunderstorms are
possible across most of the area within mainland Puerto Rico, but
southern areas should receive minimal to no rain at all. Moisture
levels are expected to peak next Tuesday, which models guidance
suggests may be the most active day of the short-term period. Please
note that due to saturated soils and much above normal river
streamflows, any period of moderate to locally heavy rain 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 and to monitor the forecast for future
updates.

Temperature-wise, they will stay in the upper 80s to low 90s along
the coastal/urban areas and in the upper 70s to low 80s along the
higher terrains. Combined with above-than-normal moisture, heat
indices may reach 100F across coastal/urban areas of Puerto Rico
and the U.S. Virgin Islands through the period.

.LONG TERM...Thursday through Monday

The mid to upper-level trough will continue moving away from the
region on Thursday, leaving the islands in a less favorable
position for organized convection. A mid to upper-level ridge will
try to build over the Northeast Caribbean Friday into the
weekend, which may further decrease local instability, potentially
bringing relief from the current weather conditions.

At the surface, GFS Total Precipitable Water guidance suggests
values returning to the typical values for this time of year from
Thursday onward. However, patches of increased moisture may arrive
occasionally. Regardless of whether we observe a mixture of
sunshine and clouds each day, strong afternoon convection could
develop due to local effects and sea breeze variations each day.
Additionally, due to the atypical high sea surface temperature,
the advection of a cooler air mass across the warmer waters may
result in frequent nighttime showers, reaching the windward
sections each night.

Temperature-wise, 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.


&&

.AVIATION...
(06Z TAFS)

Mostly VFR conditions expected for most TAF terminals this morning
but VCSH should continue near TJSJ. The potential for VCTS and
showers are expected to increase around 14Z across USVI and after 16-
18Z in PR sites. VCTS/TSRA may continue to promote tempo MVFR to
brief IFR conditions later today. E to NE surface winds at 10-15
kts, and then becoming lighter and more variable at night.

&&

.MARINE...

A surface high-pressure building across the Western Atlantic will
push a surface trough further east away from the Northeast
Caribbean, promoting light to moderate trade winds. From late
Tuesday night onward, pulses of northeasterly swell will spread
across the regional waters. Afternoon convection may result in
strong thunderstorms across the coastal sections of north and
western PR each day.

&&

.BEACH FORECAST...

Expect seas to be around 3 feet or less across most of the local
beaches in the Atlantic, mainly from the east at 6 to 7 seconds,
while across the Caribbean, seas will range up to 2 feet from the
east at 6 seconds. Therefore, we expect a slight risk of strong
rip currents through mid-week.

Pulses of northeast swells, with wave periods of 10 to 13 seconds,
will increase the risk of rip currents between moderate and high
from late Tuesday into next weekend across the north and east-
facing beaches of PR and the USVI.

&&

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

$$

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