332
FXCA62 TJSJ 181855
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
255 PM AST Sat Oct 18 2025

...New SHORT TERM, AVIATION, MARINE, BEACH FORECAST...

.KEY MESSAGES...

* Periods of heavy rainfall may cause urban and small-stream
  flooding, mainly across the interior and north-central areas of
  Puerto Rico. Expect dangerous lightning, gusty winds, and brief
  road and travel disruptions during afternoon storms.

* Occasional Showers and thunderstorms will cross the US Virgin
  Islands, producing downpours, frequent lightning, and localized
  flooding.

* Hazardous marine and coastal conditions are expected from late
  tonight into early next week along the northerly-facing beaches
  in PR and the US Virgin Islands.

* Weather conditions will gradually improve by Monday, but the
  afternoon thunderstorms and showers will affect portions of
  the islands.


&&

.SHORT TERM...
(This evening through Sunday)
Issued at 248 PM AST Sat Oct 18 2025

Thunderstorms persisted over St Thomas and St John early this
morning, with rainfall amounts recorded by local weather stations
ranging from 1 to 2.25 inches. A Flash Flood Warning and Flood
Advisories were issued, respectively. Additionally, thunderstorms
developed across the regional waters, creating hazardous
conditions for mariners. Then, early this afternoon, thunderstorms
developed across portions of PR, producing downpours, frequent
lightning, and gusty winds. Heat index values across the islands
were mainly between 100 and 106 degrees Fahrenheit, with isolated
higher amounts.

A nearly stationary frontal boundary interacting with deep
tropical moisture will maintain unsettled weather across the
northeastern Caribbean. PWAT values are above normal climatology,
with RH values confirming saturation at mid-levels. Additionally,
lapse rates are indicative of a strong instability, which will
persist toward early Monday. Thus, afternoon convection will form
today, creating frequent lightning, gusty winds, and heavy
rainfall near thunderstorm activity. We cannot rule out showers
and thunderstorms developing over the surrounding waters of the US
Virgin Islands, moving inland later this afternoon or during the
overnight hours. As a result, enhanced convergence between the
weak frontal boundary north of the area and the return of the
east-southeasterly flow could produce another round of showers or
training storms over the windward portions of PR and the US Virgin
Islands.

As 925 mb winds strengthen from the southeast, increased moisture
will foster showers and thunderstorms across the northern slopes
and coastal plains by Sunday afternoon. Afternoon heating and sea-
breeze convergence may lead to intense, slow-moving storms over
the interior and north-central Puerto Rico, potentially causing
urban and small-stream flooding. Although instability is high
early in the day, mid-level warming will likely weaken convective
strength later.

On Monday, as the atmosphere aloft stabilizes under a moist
atmosphere, we expect another round of afternoon convection mainly
across western and interior PR. Although the overall coverage of
rainfall is expected to be lower, there remains a possibility of
isolated heavy downpours, lightning, and brief gusty winds.

&&

.LONG TERM...Tuesday through Friday...
Issued at 248 PM AST Sat Oct 18 2025

Tuesday is expected to be the driest and most stable day of the
long-term period, as model guidance indicates precipitable water (PWAT)
values decreasing to around or slightly below normal for this
time of year. This drier and more stable air mass will help
suppress widespread convective activity, leading to mostly fair
weather conditions. However, localized afternoon showers cannot be
ruled out, mainly across the interior and western sections of
Puerto Rico due to daytime heating and local effects. Flooding
potential remains minimal through this period.

Wednesday will still be a generally fair day, with conditions remaining
relatively stable during the morning hours. However, as the day
progresses, a gradual increase in moisture content and mid-level
humidity is expected, resulting in a higher potential for
afternoon showers across portions of the interior and western
Puerto Rico. This trend marks the beginning of a slow transition
toward a wetter pattern.

From Thursday onward, the forecast becomes increasingly dependent on
the evolution of a system currently being monitored by the
National Hurricane Center (NHC). At this time, the long-term
forecast leans toward the GFS solution, which depicts a wetter
pattern developing from Thursday into the weekend. The NHC
currently assigns this disturbance a 0 percent chance of
development within the next 48 hours and a 30 percent chance
within the next 7 days.

It is important to note that forecast confidence decreases
significantly after Thursday, as there remains high uncertainty and
notable discrepancies among model solutions regarding the
development and possible impact for Puerto Rico and the U.S.
Virgin Islands. Regardless of development, an increase in moisture
and instability could lead to wetter and potentially unsettled
conditions late in the week.

Residents and visitors are advised to monitor the latest forecasts
and updates from the National Weather Service and the National
Hurricane Center for any significant changes.

&&

.AVIATION...
(18Z TAFS)
Issued at 248 PM AST Sat Oct 18 2025

(18Z TAFs)

Mostly VFR conds are exptd across all terminals. -TSRA/+TSRA across
the CWA through 18/22z will promote VCTS mainly over JBQ, JPS, ISX,
IST, and JSJ. TSRA nearby JSJ could reduce CIGs/VIS and promote MVFR
conds until 18/22z. Winds will become light and VRB after 18/22z,
increasing from the SE btwn 9 - 12 kt by 19/12 - 19/14z.

&&

.MARINE...
Issued at 248 PM AST Sat Oct 18 2025

A lingering frontal boundary and plenty of moisture will promote
shower and thunderstorm activity across the regional waters and
passages through at least late tonight. A long period northerly
swell, propagating across the Atlantic Ocean, will slowly
deteriorate the marine and coastal conditions later tonight
through early next week. Thus, hazardous marine conditions are
anticipated from around Sunday morning onward. Please, continue
to monitor the forecast updates over the coming days.

&&

.BEACH FORECAST...
Issued at 248 PM AST Sat Oct 18 2025

A moderate to high risk of rip currents will persist across the
north and east-facing beaches through this evening. Then, a long
period northerly swell will gradually increase from late Saturday
morning into early Sunday morning, reaching its maximum values
around Sunday afternoon and overnight. This swell will create
dangerous breaking waves and life-threatening rip currents along
the west, north, and eastern beaches of the islands from Sunday
into early next week.

High surf conditions and minor coastal flooding are likely by
Sunday afternoon, and may extend into the early part of next week.
Overall, dangerous swimming conditions, minor beach erosion, and
life-threatening rip currents are expected from this weekend into
early next week.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through late Sunday night for PRZ001-002-
     005-008-010-012.

VI...None.
AM...None.
&&

$$

MORNING CREW...CAM/MNG
EVENING CREW...ICP/YZR