Bda Corea, Puerto Rico Weather Forecast Discussion

217
FXCA62 TJSJ 191819
AFDSJU
Area Forecast Discussion
National Weather Service San Juan PR
219 PM AST Fri Sep 19 2025
.KEY MESSAGES...
* A warm trend weather is forecasted due to increased humidity
  and a southeasterly wind flow, promoting heat indices between
  108 and 111 degrees.
* Afternoon shower activity is expected each day across the interior-
  west and northwest sections of the island, inducing an elevated
  flood threat and a limited lightning threat.
* A variable weather pattern is expected for the US Virgin
  Islands during the weekend, with shower activity during the
  morning and early evening hours.
&&
.SHORT TERM...Rest of today through Sunday...
Mostly cloudy skies prevailed across the islands today. Showers
and thunderstorms developed earlier in the day, and continued into
the mid-afternoon hours. The Doppler radar estimated up to 2
inches of rain across most of central, western, and northern
Puerto Rico through 2 PM AST. Across the U.S. Virgin Islands,
isolated thunderstorms developed just north of St. Croix early in
the afternoon hours. Southerly winds prevailed up to 10 mph with
sea breeze variations. Temperatures were from the mid-80s to low
90s across most lower elevations of the islands.
For the rest of this afternoon, thunderstorms will continue to
affect central and northern Puerto Rico, where flood concerns will
continue through at least the evening hours. A mid-to upper-level
trough north of the region will continue to support a wet weather
pattern through the weekend, with global models suggesting
precipitable water values lingering above 2 inches through Sunday.
Steering winds will continue light with a southerly component for
most of the period, until late Sunday when weak trades return
across the northeastern Caribbean. Therefore, expect early morning
showers to develop near the USVI and along the south and east
sections of PR, followed by strong afternoon thunderstorms over
the Cordillera Central and the northern half of PR. Urban and
small stream flooding will be the main weather hazards, including
possible isolated flash floods and landslides in areas of steep
terrain. Frequent cloud to ground lightning strikes and gusty
winds cannot be ruled out with these thunderstorms each afternoon.
.LONG TERM...Monday through Friday...
At the start of the upcoming workweek, light winds will prevail,
gradually shifting from southeasterly to easterly throughout the
day. This shift will be driven by a surface high-pressure system
dominating the Central Atlantic. Based on the latest model
guidance, Monday is expected to have the lowest precipitable water
content of the forecast period, with values ranging from slightly
below average to near seasonal levels. Additionally, drier air is
anticipated in the mid to upper levels of the atmosphere compared
to recent days. Temperature-wise, forecast data indicates that
925 mb temperatures will remain nearly two standard deviations
above normal on Monday, followed by a gradual cooling trend. Under
these conditions, expect morning showers over windward areas of
the islands, with afternoon showers and isolated strong
thunderstorms developing across interior and western Puerto Rico.
These will be driven by diurnal heating, available moisture, and
local effects.
By Tuesday, a transition to a wetter and more unstable pattern is
expected to evolve. An approaching wind surge will increase wind
speeds and moisture levels, leading to higher chances of rainfall
through the remainder of the forecast period. Model guidance
suggests a rapid rise in PWAT values, peaking around 2.0 to 2.25
inches, well above climatological norms for this time of year.
Around Wednesday into Thursday, a tropical wave currently being
monitored by the National Hurricane Center is forecast to approach
the region, further enhancing the wet pattern. As of now, the
wave is located just off the west coast of Africa, with a low
formation chance in the next 48 hours (near 0%) and a 20% chance
over the next 7 days. Aloft, some troughiness should be present
combined with low level southeasterly flow driven by the Atlantic
surface high pressure system. This will continue to advect
tropical moisture into the region through Friday maintaining the
wet pattern. Expect and elevated flood risk each day, likely
including rapid river rises and landslides. Current model guidance
suggests the system may develop after moving away from our area.
We will continue to monitor this evolving situation closely and
provide updates as necessary.
&&
.AVIATION...
(18z TAFs)
Tempo MVFR conds expected at TJBQ/TJSJ thru 19/21z due to TSRA.
Elsewhere, mostly VCTS thru this evening, and VCSH across all
terminals overnight. VFR conds expected to prevail til around
20/16z. The 19/12z TJSJ sounding indicated SE to S winds up to 14
kt blo FL070.
&&
.MARINE...
A surface high pressure, in combination with Tropical
Storm Gabrielle located about 550 miles east-northeast of the
northern Leeward Islands, will continue to result in a gentle to
light southeasterly wind flow across the local waters through the
rest of today into the weekend. As a result, seas will range from 2
to 5 feet across most of the waters. Localized hazardous marine
conditions are possible due to showers and thunderstorms that could
produce locally higher seas and gusty winds. A long-period
northeasterly swell generated by Tropical Storm Gabrielle, currently
moving over the central Atlantic, will reach the local waters and
passages during the weekend. However, seas are forecast to remain
below Small Craft Advisory criteria.
&&
.BEACH FORECAST...
A moderate rip current risk persists today along northwest Puerto
Rico, with a low risk elsewhere, though dangerous currents remain
possible near piers, reefs, and jetties. This risk will increase
again from Saturday into early next week as swells from Tropical
Storm Gabrielle arrive. Strong afternoon thunderstorms would
trigger the lightning threat along the northern coastal side.
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&
$$
SHORT TERM/AVIATION...DSR
KEY MESSAGES/BEACH/MARINE...LIS
LONG TERM...YZR

NWS SJU Office Area Forecast Discussion