155
FXCA62 TJSJ 140903
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
503 AM AST Sat Jun 14 2025

.KEY MESSAGES...

* Shower activity will be less widespread today compared to Friday,
  though isolated afternoon showers or thunderstorms may still
  develop, mainly across interior and western Puerto Rico.

* Hazy skies will gradually increase from Sunday onward, with the
  peak of the Saharan Air Layer expected Monday and Tuesday.
  Despite the haze, above-normal moisture and atmospheric
  instability are also likely, which may still support some
  convective activity, especially from Sunday through early next
  week.

* Elevated fire danger conditions will persist today across southern
  Puerto Rico, especially across the southwestern coastal plains and
  nearby hills. Fuels remain critically dry, and fire activity was
  reported on Friday. Residents are urged to avoid outdoor burning
  and remain alert.

&&

.SHORT TERM...Today through Monday...

Mostly fair weather conditions prevailed last night, with few
passing showers moving across the local waters. Breezy conditions
continued during the night, with maximum wind gusts up to 20 mph
based on station reports in coastal areas across the CWA. Minimum
temperatures remained similar to yesterday`s, with urban and coastal
areas between the mid 70s and lower 80s and interior portions in the
low to mid 60s.

The current satellite-derived product shows abundant moisture
content south of the CWA due to a tropical wave that continues its
way over the Caribbean Basin. The broad surface high pressure system
is expected to slowly migrate eastward, promoting E-SE winds and
breezy conditions prevailing for the rest of the forecast period.
The drier air mass will continue filtering into the region,
promoting stability aloft and inhibiting deeper convection activity.
However, an upper-level trough should established north of the CWA
by Sunday, becoming a cut-off low by the beginning of the workweek.
This can be seen in the latest deterministic model guidance from GFS
and ECMWF, where ensemble members portray below-normal (1.38 inches
today) to near above-normal (1.87 inches) PWAT values. The 500 mb
moisture content is expected to rise up to 90%, as the upper level
trough settles. This will also increase instability aloft, as 500 mb
temperatures should cool (around -8 Celsius), which increases the
chances of thunderstorm activity. Additionally, the Galvez-Davison
Index highlights the potential of thunderstorms approaching the CWA
by Sunday evening into the early morning, as well as the deep
convection activity in the afternoons. Although low concentrations
of Saharan Air Layer (SAL) are expected to approach the local
islands by Sunday evening, conditions should remain favorable for
deep convection activity.

Overall, afternoon convection is expected today over portions of
interior and western Puerto Rico, with few showers and isolated
thunderstorms affecting the aforementioned areas. The frequency of
showers and thunderstorms should increase by Sunday afternoon, with
the approach of the upper-level trough. The flood threat will rise,
mainly for western/northwestern Puerto Rico in the afternoons, while
eastern portions will be affected mainly from Sunday evening through
Monday morning. Urban and small stream flooding is the most likely
scenario, with a low chance of isolated flash floods, citizens
should stay weather alert.

Seasonal temperatures and increasing moisture content will maintain
a limited heat threat through the forecast period, mainly over
coastal areas and lower elevations. With the arrival of the
suspended SAL, areas not experiencing rainfall activity will likely
have hazy skies, reduced visibility, and a slight degradation in air
quality, affecting people sensitive to these particles.

.LONG TERM...Tuesday through Saturday...

The long-term forecast begins wet and unstable, as a retrograding
TUTT dominates the upper-level dynamics through at least the end of
the workweek. Model guidance suggests cold air advection at mid-
levels as the TUTT meanders over the region, with the median
quartile of the combined ECMWF and GFS ensembles indicating 500 mb
temperatures dropping to between -8C and -9C by Tuesday. These
conditions will lead to steep low- to mid-level lapse rates, along
with below-normal 250 mb height fields, which are favorable for deep
convective activity.

These favorable dynamics will coincide with above-normal columnar
moisture across the region. This pattern could lead to near-severe
thunderstorms, particularly when combined with diurnal heating and
orographic lifting. Potential impacts include frequent lightning,
gusty winds, and small hail, especially at higher elevations in
Puerto Rico during the afternoon hours. A primary limiting factor
will be the presence of suspended Saharan dust, which could slightly
reduce relative humidity around the 700 mb layer. While this may
limit the areal coverage of showers and thunderstorms, localized
strong activity remains likely. Additionally, the Saharan dust may
enhance lightning activity within thunderstorms.

By Saturday, even though the TUTT moves farther northward, marginal
instability will remain in place. At low levels, another tropical
wave will maintain above-normal moisture over the northeastern
Caribbean on Saturday. As a result, a limited to elevated flooding
threat is expected each day, particularly over the interior and
western portions of Puerto Rico during the afternoon hours. The most
active day is expected to be Tuesday, as it coincides with the most
favorable positioning of the TUTT over the region.

Aside from the likelihood of shower and thunderstorm activity, the
presence of above-normal moisture combined with near to slightly
above-normal temperatures could result in heat index values reaching
levels associated with a limited to localized elevated heat threat,
particularly across urban and coastal areas of the islands. This
risk may increase toward the end of the workweek, as cloud cover
decreases over the area. Residents are advised to stay hydrated,
avoid prolonged outdoor activities during peak heating hours, and
check on vulnerable individuals such as the elderly and young
children.


&&

.AVIATION...
(06z TAFs)

Mainly VFR conds across all TAF sites. Aftn convection will mostly
concentrate across western PR, but VCTS over TJBQ remains likely
around 14/18z. E winds will dominate the fcst pd, btwn 12 - 18 kt,
and gsty winds btwn 20 - 25 kt after 14/13z, slowing down btwn
7-10 kt around 14/23z.

&&

.MARINE...

The surface high pressure north of the region will gradually shift
east in the coming days. This will result in some fluctuations in the
wind pattern over the region. But overall, expect moderate to
locally fresh east to east southeast winds across the northeastern
Caribbean through mid-week of next week, leading to choppy seas. A
tropical wave south of the local islands will continue to move
westward today, followed by another wave expected to approach the
region by mid-week of the upcoming workweek. In the meantime,
increasing moisture and instability associated with an upper-level
trough will likely result in a rise in thunderstorm activity late
this weekend into early next week.

&&

.BEACH FORECAST...

Moderate rip current risks will persist along many north-, east-,
and south-facing beaches over the coming days due to ongoing breezy
conditions. This is especially true for locations exposed to open
waters. While western beaches tend to be more protected, caution
is still advised near jetties, piers, and channels where stronger
currents can still develop.

Scattered showers or isolated thunderstorms may develop through the
weekend, particularly over western Puerto Rico. Visitors should
remain weather-aware, as any storm could bring dangerous lightning.
An increase in upper-level moisture and atmospheric instability may
support more widespread thunderstorm activity by late weekend into
early next week.

Beachgoers are reminded to swim near lifeguards whenever possible,
steer clear of strong surf, and stay updated on evolving weather
conditions.

&&

.FIRE WEATHER...

Todays weather conditions are expected to remain largely similar to
yesterday, with a slight increase in dryness across southern Puerto
Rico. Very dry fuels continue, as indicated by elevated KBDI values,
574 at Cabo Rojo and 611 at Guanica, both signaling critical fire
weather conditions. These values, in conjunction with continued
rainfall deficits over the past 30 to 60 days across this region,
point to enhanced wildfire potential.

Breezy to locally windy conditions, low relative humidity, and poor
fuel moisture recovery will continue to support rapid fire spread,
especially across the southwestern coastal plains and adjacent
hills. Notably, fire activity was reported in these areas yesterday,
and similar activity is possible again today under these conditions.

While dry and breezy conditions will persist through today, a
gradual increase in moisture is expected to begin on Sunday, which
may begin to ease fire weather concerns in the coming days.
Nevertheless, for today, elevated fire weather remains a concern,
and a Fire Danger Statement is in effect for the southern coastal
plains and hills of Puerto Rico.

Residents and land management officials should continue to exercise
caution and follow any guidance in place. Refer to the latest Fire
Danger Statement (RFDSJU) for more information.

&&

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

$$

SHORT TERM/AVIATION...MNG
LONG TERM/MARINE/FIRE...CVB