Urb Rancho Bonito, Puerto Rico Weather Forecast Discussion

956
FXCA62 TJSJ 131913
AFDSJU
Area Forecast Discussion
National Weather Service San Juan PR
313 PM AST Sat Sep 13 2025
.KEY MESSAGES...
* Afternoon showers and thunderstorms will persist this afternoon,
  with a tropical wave bringing increased shower activity late
  tonight into early Sunday across eastern Puerto Rico. Local
  impacts include ponding of water on roadways, quick river rises,
  landslides in vulnerable areas, and frequent lightning.
* Cloud coverage from the tropical wave may limit the usual
  afternoon activity on Sunday, but periods of heavy showers are
  still possible.
* Heat risk continues each day, with heat index values above 100F
  across coastal areas, though Sundays clouds may slightly hinder
  the highest values.
* A wetter and more unstable pattern is expected mid to late week as
  above-normal moisture combines with a deep-layer trough,
  heightening the threat for flooding rains, frequent lightning,
  river rises, and landslides.
* In the U.S. Virgin Islands, expect increased showers late
  tonight into Sunday, continued dangerous heat risk each day, and
  unsettled weather mid to late week with potential for heavy
  rains and frequent lightning.
&&
.SHORT TERM...Tonight through Monday...
Diurnal heating, local orographic effects, available moisture and
troughiness over the region (an upper trough is to our northeast)
helped develop convection by late morning. Lines of showers and
started to develop from the USVI, Vieques and Culebra by around 10
AM, before developing into t-storms. Convective t-storms then
developed by 1030 AM over Canovanas and Carolina and over Salinas
and Coamo. As the day progressed, shower and t-storm activity spread
to interior, northern, north-central, northwestern and western
Puerto Rico where strong t-storms are currently affecting those
areas. As of 230 PM, radar estimated accumulations indicated that
Canovanas, Carolina, Salinas, Aibonito, Ciales, Florida, Manati,
Barceloneta, Utuado, Lares and Isabela, saw at to above 2 inches of
rain. By 230 PM, Florida, Arecibo and Canovanas saw the highest
radar estimated accumulations with 4.16 in, 3.44 in and 3.20 in,
respectively. Heat indices reached Heat Advisory Criteria but
quickly decreased over most areas as the late morning to afternoon
convection developed. Under east-southeast steering flow this
convective activity will gradually dissipate and/or move offshore we
head towards the evening.
However, a tropical wave, currently over the Lesser Antilles and
eastern Caribbean Sea, will continue to move eastward and approach
the region later tonight. It`s moisture field, with precipitable
water values above 2 inches and reaching 2.25 inches, will cross the
Anegada Passage and reach the USVI late tonight and into the
overnight hours. Late in the overnight hours and to start tomorrow
morning, the moisture field from this tropical wave will reach
eastern Puerto Rico. As this wave approaches the aforementioned
regions will see an increase in showers and isolated t-storms during
the overnight to morning hours. Afternoon showers and t-storms are
forecast to develop once again across central PR to W-NW PR, as well
as downwind of El Yunque and the USVI. A limited to elevated
flooding risk remains for tomorrow, although limiting factors to
rainfall accumulations could be extended cloud cover during the
morning and increased winds (faster moving showers and t-storms).
Diurnal heating, instability from the wave, local effects, and
nearby troughiness will serve to support this afternoon activity and
redevelopment of its outflows. The wave`s moisture field will
gradually leave the region during the overnight hours Sunday to
Monday. A dry slot will then move over the area, but it will be
short lived as another patch of moisture approaches followed by a
patch of moisture. This patch of moisture has PWAT values of around
2 inches and will serve to enhance rain and t-storm potentials
during the day, particularly during afternoon convection. A tropical
wave will also approach the area to end the period and reach the
islands to start the long term period. 925 mb temperatures are
expected to be at normal values during the short term period,
Limited to elevated heat risks are expected at more prone sectors
but afternoon convection will still serve as relief.
.LONG TERM...Tuesday through Saturday...
./FROM PREV DISCUSSION...Issued at 347 AM AST Sat Sep 13 2025/
Unsettled weather conditions are expected during the workweek as a
couple of tropical waves moves into the region. The first wave
moves in Tuesday and Wednesday, bringing an increase in showers
across the Virgin Islands, and then this cluster of moisture will
reach Puerto Rico. As a result, the frequency of showers and
thunderstorms will increase. Areas that receive heavy rain will
experience flooding, and rapid river rises. Lightning strikes will
remain a concern for those in the exterior at the times of
thunderstorms. Instability will increase further on Thursday as an
upper level low moves just north of the islands. By the end of the
period, yet another tropical wave moves close to the islands,
bringing intermittent periods of showers into the region.
Areas that do not experience rain or cloudiness, however, will
continue to observe elevated heat indices, much above normal
values. As it has been consistently hot for the past couple of
week, those without effective cooling or adequate hydration will
could be affected.
&&
.AVIATION...
(18Z TAFS)
Mainly VFR to brief MVFR conditions over the terminals or their
VCTY. Persisting through 13/22Z for TJBQ and possibly TJSJ.
SHRA/TSRA over the vicinity of TJPS/TIST/TISX will move away from
them during the afternoon. Sfc winds from the ESE up to 16 mph, with
higher gusts and sea breeze variations, decreasing after 23Z and
picking up again after 14/13Z. A tropical wave will approach the area
late tonight and promote VCSH/VCTS over TISX/TIST beginning at
around 14/02Z and possibly over TJSJ by 14/12Z.
&&
.MARINE...
A surface high pressure over the central Atlantic and a front over
the western Atlantic will promote light to moderate east to
southeast winds through this afternoon, increasing to moderate to
fresh tonight through early next week as a tropical wave crosses the
region. Afternoon showers and thunderstorms are likely each day,
particularly over the western waters of Puerto Rico and the Mona
Passage. The tropical wave will bring additional showers and
thunderstorms across the local waters on Sunday.
&&
.BEACH FORECAST...
The risk of life-threatening rip currents will increase to moderate
beginning Sunday and persist through most of the workweek,
particularly for northern and eastern exposed beaches of Puerto Rico
and U.S. Virgin Islands.
Even with a low risk, life-threatening rip currents can still occur
near groins, jetties, reefs, and piers, so beachgoers are advised to
exercise caution at all times.
Additionally, thunderstorms are likely during the afternoon hours,
producing dangerous lightning strikes; be prepared to seek shelter
if thunder is heard.
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&
$$
SHORT TERM/AVIATION...MRR
LONG TERM...ERG
MARINE/BEACH FORECAST...CVB

NWS SJU Office Area Forecast Discussion