171
FXCA62 TJSJ 061810
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
210 PM AST Tue May 6 2025

.KEY MESSAGES...

* Showers and thunderstorms will continue to pose an elevated
  threat of flooding over the next 24-36 hours, especially
  Wednesday afternoon.

* Due to ongoing soil saturation conditions, the risk of
  mudslides/landslides persists along the steep terrains.

* Water surges and elevated river levels pose a heightened risk
  of rivers overflowing their banks, especially with any
  additional rainfall.


&&

.SHORT TERM...Tonight through Thursday...

Radar and satellite analysis showed fair conditions across the
region this morning, with a thin layer of upper-level clouds from
a trough to the west. Despite this, temperatures have reached the
mid to upper 80s, accompanied by light and variable winds,
primarily influenced by the sea breeze. Aside from showers and a
few thunderstorms over the waters and downstream of the northern
U.S. Virgin Islands, Culebra, and Vieques, which began developing
around 10:30 AM AST, showers developed downstream from El Yunque
into nearby counties around noon. While the upper- level cloud
layer may slightly delay afternoon convection, the forecast
remains on track for active weather later this morning into early
evening. Increased shower and thunderstorm activity is expected,
particularly across central Puerto Rico, where significant
rainfall and flooding impacts have been observed in recent days.

A deep-layer trough will continue to influence the region through
the forecast period, maintaining favorable conditions for
thunderstorm development through Wednesday. The most active
periods are expected in the afternoon and early evening,
especially across the interior and western areas, where daytime
heating and sea breeze convergence are most effective. Elevated
moisture (with PWATs between 1.62.0 inches), strong upper-level
divergence, and cooler-than-normal 500 mb temperatures will
support this activity. Light east to east-northeasterly winds
(510 knots), influenced by a surface trough to the north, will
further enhance local convergence. Although convection generally
peaks during the afternoon, overnight and early morning
thunderstorms may develop across eastern Puerto Rico and the local
islands, where flooding impacts remain possible due to favorable
upper-level support and abundant moisture.

Starting Thursday, the trough will gradually shift eastward,
bringing drier and more stable conditions. PWATs will drop below
climatological normals (under 1.5 inches), and rapid mid-level
warming will reduce instability. While the absence of a trade wind
inversion will allow for isolated convection from daytime heating
and local effects, any resulting activity should be weaker and
more localized. Temperatures will remain near or slightly below
normal, offering some relief from typical May heat. Although no
widespread alerts are in effect, the region remains at heightened
risk for flash flooding, rapid rises in rivers and streams, and
mudslides, particularly in areas of steep terrain, due to the
saturated soils from prolonged rainfall. These risks will continue
through Wednesday, but conditions will gradually improve by
Thursday. Refer to the Experimental Graphical Hazardous Weather
Outlook for updated hazard information:
https://www.weather.gov/erh/ghwo?wfo=sju.

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

From previous discussion...issued at 459 AM AST Tue May 6 2025

When the upper-level trough exits the region by Friday, moving
eastward into the Atlantic Ocean, model guidance indicates dry air
intrusion above 700 MB over the Northeast Caribbean. This air
mass aloft will induce subsidence, limiting the potential for
widespread rain activity each day. However, at low levels,
sufficient tropical moisture interacting with the easterly winds
will continue to promote periods of showers across the windward
locations in the US Virgin Islands and Puerto Rico, mainly due to
low-level convergence, followed by afternoon convection over the
interior and western Puerto Rico due to sea breeze, local effects,
and diurnal heating each day.

Winds will increase by the end of the week as a surface high-
pressure building across the Central Atlantic tightens the local
pressure gradient. An advective pattern may increase the frequency
of the typical passing showers across the windward locations,
moving further inland across PR due to these rising winds.

Model guidance shows another deep trough approaching the
Northeast Caribbean by next Tuesday, potentially increasing the
instability over the region and the likelihood for thunderstorm
development with flooding rain.


&&

.AVIATION...
(12Z TAFs)

VFR conditions are expected to prevail across all TAF sites
through at least 06/17Z. After that, periods of MVFR conditions
are likely at TJBQ due to SHRA/TSRA through 06/22Z. TJSJ and the
USVI terminals may also experience MVFR conditions after 06/22Z as
shower activity increases. VCSH/VCTS are possible across all
terminals after 07/16Z. Winds will remain from the east-northeast
at 1015 knots with a strong sea breeze influence, becoming light
and variable after 06/22Z, then increasing again to 1015 knots
after 07/14Z. Higher gusts are possible in and near TSRA.


&&

.MARINE...

A broad surface high pressure extending into the Central Atlantic,
in combination with an induced surface trough northeast of the
region, will result in light to moderate easterly winds across the
local waters today, then becoming light to gentle through the end of
the workweek. Mariners can expect seas between 2 to 4 feet,
occasionally 5 feet, for the next several days. Occasional
thunderstorms are likely across the regional waters, especially in
the afternoon, resulting in dangerous conditions for mariners.


&&

.BEACH FORECAST...

Beachgoers can expect a low risk of rip currents across the local
beaches. However, remember that rip currents often occur near
groins, jetties, reefs, and piers. The risk of rip currents will
become moderate on Sunday and Monday next week.


&&

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

$$

SHORT TERM/AVIATION...ICP
PUBLIC...MNG