947
FXCA62 TJSJ 131700
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
100 PM AST Fri Jun 13 2025

.KEY MESSAGES...

* Diurnally induced afternoon showers and isolated thunderstorms
  are expected to develop mainly over western PR each afternoon
  through Saturday. The flood risk increases in general across the
  rest of PR from Sunday through Tuesday due to an upper-level
  trough.

* Elevated fire danger risk expected through Saturday, increasing
  wildfire riskespecially in southern Puerto Rico. Please avoid
  outdoor burning and stay alert.

* Hazy skies expected to return once again on Sunday due to a weak
  Saharan Air Layer. However, the overall moisture content will
  increase due to the proximity of the upper-level trough.


&&

.SHORT TERM...Today through Sunday...

Sunny to partly cloudy skies and hazy conditions were observed
once again today across Puerto Rico and the U.S. Virgin Islands.
Showers were developing around noon over west/southwest Puerto
Rico, and from streamers downwind of the U.S. Virgin Islands.
Stronger showers with isolated thunderstorms are expected to
develop over western PR and over the Mona Passage later this
afternoon. Maximum temperatures were from the upper 80s to low
90s across most lower elevations of the islands, and from the
upper 70s to mid-80s across the higher elevations. The wind was
from the east to northeast between 15 and 25 mph with sea breeze
variations and higher gusts across coastal areas.

A broad surface high pressure north of the region will remain in
place for most of the short-term period, this will continue to
promote moderate to fresh trade winds across the region. However,
patches of shallow moisture embedded in these trades will reach
the islands from time to time. A departing Saharan Air Layer (SAL)
and a drier mid-to upper-level air mass will continue to promote
overall fair weather conditions across the islands, with the
exception of afternoon showers and isolated thunderstorms over
western PR today and Saturday. The overall precipitable water
content is expected to remain below normal levels, around 1.50
inches each day.

A weaker SAL event is expected on Sunday, but conditions will
gradually become more favorable for shower and thunderstorm
development as an upper level-through develops just north of the
area. This trough is expected to deepen and form a closed low
northwest of the region by Saturday afternoon into Sunday morning.
Temperatures at 500 mb will drop to near -8C to -9C, and
moisture will increase in the mid-to upper-levels. PWAT values are
expected to increase around 2.00 inches, which is above normal
levels for this time of the year. Therefore, a wetter and more
unstable weather pattern is expected on Sunday afternoon, and will
likely continue through early next week.

Minimum temperatures are expected to range from the mid-70s and low
80s across the lower elevations of the islands to the mid-60s across
the higher elevations of central PR through at least tonight, and
slightly cooler during the weekend. Maximum temperatures will
continue to range from the upper 80s to low 90s across coastal and
urban areas of the lower elevations of the islands, to the mid-70s
and low to mid-80s across the higher elevations. Heat indices
will likely range between 102F-106F each day in the lower elevations
of western and north central PR.

.LONG TERM...Monday through Friday...

/From prev discussion issued at 500 AM Fri Jun 13 2025/

The workweek will begin wet and unstable, with abundant moisture
and atmospheric instability supporting frequent showers and
thunderstorms through at least Wednesday. An upper-level low
lingering over the region will keep mid-level temperatures cooler
and weaken the trade wind cap, allowing rainfall potential to
rise, especially on Monday and Tuesday, when precipitable water
values are forecast to exceed 2.0 inchesabove normal for this
time of year. Moisture levels are expected to decrease to near-
normal values, ranging from 1.5 to 1.9 inches, for the remainder
of the week, with Thursday night likely being the driest period.

At the surface, a strong Bermuda-Azores High will maintain
moderate to locally strong easterly winds, producing breezy to
windy conditions, especially along the coast and exposed areas.
Temperatures will remain cooler through Tuesday, both during the
day and at night, before gradually warming from Wednesday onward
as sunshine increases and rainfall chances decrease.

Showers and isolated thunderstorms will be most frequent and
organized early in the week. Overnight and early morning activity
will primarily impact eastern Puerto Rico and the U.S. Virgin
Islands, shifting to central, western, and northern Puerto Rico,
including parts of the San Juan metropolitan area, from late
morning through the evening. Heavy or prolonged rainfall may lead
to urban and small stream flooding, as well as localized flash
flooding. As soils become saturated, the risk of landslides will
increase. Later in the week, conditions are expected to return to
a more typical pattern of scattered showers.

Overall, risks from excessive heat, strong winds, and lightning
remain low. However, the elevated threat of heavy rainfall and
localized flooding will continue through midweek before gradually
easing. And importantly, no tropical cyclone formation are
expected over the next seven daysproviding us with a much-needed
window of calm and peace of mind.


&&

.AVIATION...

(18Z TAFs)

Mainly VFR conditions are expected to prevail across all terminals
through the forecast period. However, fm 13/18z-22z, locally induced
SHRA/TSRA expected to develop over western PR, which should cause
mostly VCTS at TJBQ. HZ due to Saharan dust will continue to
diminish across the local area, and VSBY should remain P6SM.
The 13/12z TJSJ sounding indicated ENE winds up to 19 kt blo
FL050.


&&

.MARINE...

The Bermuda-Azores High will continue to promote moderate to
locally fresh easterly winds across the northeast Caribbean
through early next week, leading to choppy seas. A tropical wave
will move south of the local islands from today through Saturday,
followed by another wave expected to approach the region by mid-
week. 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...

Breezy conditions will keep a moderate risk of dangerous rip
currents along most north, east, and south facing beaches over
the next few days, especially in areas exposed to open water.
Western beaches that are more sheltered will have a lower risk,
but stronger currents can still form near piers, jetties, and
channels. Only a few showers or storms are expected today and
Saturday, but anyone visiting western Puerto Rico should stay
alert for lightning from isolated thunderstorms. Increasing
moisture and instability from an upper-level system will likely
lead to more thunderstorm activity late this weekend into early
next week, so keep an eye on the forecast.

Looking ahead, a high risk of rip currents is possible around
mid-week next week for St. Croix. Always swim near a lifeguard,
avoid strong currents, and stay alert to changing weather and
gusty winds.


&&

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

$$

SHORT TERM...DSR
LONG TERM....ICP
AVIATION...DSR