062
FXCA62 TJSJ 061847
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
247 PM AST Fri Jun 6 2025

.KEY MESSAGES...

* Above-normal moisture associated with a tropical wave, along with
  increasing instability, might result in a rise in showers and
  thunderstorms by midweek next week.

* Warmer-than-normal temperatures are likely to continue through the
  weekend across most coastal and lower elevations of the islands.

* Increasing surface winds will likely generate moderate to locally
  fresh winds, resulting in wind-driven seas by midweek next week.
  Therefore, small craft operators should exercise caution. Small
  Craft Advisories may be needed across the offshore waters.

&&

.SHORT TERM... Tonight through Sunday...

Passing showers moved mainly over the regional waters and windward
sections during the morning hours. Maximum temperatures in the urban
and coastal areas reach the lower 90s, while stations in the upper
elevations reported mid 70s to mid 80s. The 12z sounding reports
show slightly below normal PWAT values (1.31 inches) with a cap
inversion near the 700 mb layer. Additionally, the RAOB reported
seasonal 500 mb temperatures (-6.5 Celsius). Combined with diurnal
heating and local effects, it was enough to trigger convection
activity, starting around 15z over interior portions of Puerto Rico
including the San Juan Metropolitan Areas. As of 17z, rainfall
accumulations have ranged from 0.5 - 0.8 inches over Guaynabo and
Bayamon as well as in localized areas over Lares and Adjuntas. For
tonight, minimum temperatures in urban and coastal areas between low
to mid 70s, while interior sections should observe minimum temperatures between
low and mid 60s.

A variable weather pattern is anticipated for this weekend. A
surface high pressure in the Central Atlantic will continue
promoting a easterly windflow, then turning from the ESE-SE by
Saturday. As the surface high pressure strengthens, winds will
increase and promote breezy to locally windy conditions for the rest
of the forecast period. This feature will also continue steering
smoke from wildfires in Canada north of the region, but
concentrations should remain low. Based on deterministic guidance of
the GFS and ECMWF, there`s a high chance of PWAT values decreasing
below the 10th percentile (mean around 1.29 inches) due to a drier
air mass filtering into the region. However, the most likely
scenario would be similar to Friday afternoon, with rainfall
accumulations increasing the potential of flooding over interior and
western Puerto Rico but remaining localized. Additionally, steering
winds might also trigger the San Juan streamer, although the chances
of flooding will remain limited. Moisture content will gradually
increase on Saturday evening into Sunday, as a patch of moisture
approaches the local islands. Ensemble members agree that PWAT
values will increase to near above climatological normals (1.7 - 1.8
inches). This will most likely promote frequent showers over eastern
portions of Puerto Rico and the U.S. Virgin Islands during the night
and early morning, enhancing flooding potential.

With the ESE-SE winds and above-normal temperatures, a limited risk
of heat should persist for the rest of the forecast period mainly
over urban areas and lower elevations.

.LONG-TERM...Monday through Thursday...

A mid level ridge will persist over the region by early next week,
with the arrival of suspended Saharan Saharan by midweek, although
to a lesser extent than during the previous event. A surface high
over the Atlantic will continue to build during the period,
maintaining breezy to locally windy easterly, to east-southeasterly
trade winds. Precipitable water values are expected to surge to
above-normal levels, particularly on Tuesday as a tropical wave
moves across the eastern Caribbean. Despite the presence of the mid-
level ridge, the diurnal pattern will dominate, with showers likely
over the windward sectors, especially during the morning, and
afternoon showers and thunderstorms developing over interior to
western Puerto Rico. These will result from diurnal heating, sea
breeze convergence, and orographically-driven convection. Streamers
downwind of El Yunque and the local islands are also likely to
develop.

Toward the end of the long-term period, the frequency of showers is
expected to increase as an upper-level trough approaches from the
northeast. An elevated risk of flooding is forecast over interior to
western Puerto Rico each afternoon. The risk could increase for the
eastern portion of the CWA towards the end of the long-term period
with the arrival of the tropical wave and the upper-level trough.
Highs will reach the upper 80s to low 90s, with heat indices over
100 degrees. A limited heat risk will persist for most coastal and
lower elevation areas.


&&

.AVIATION...
(18Z TAFs)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. Any SHRA that develops will be brief, ESE
winds and local effects can produce VCSH near TJBQ/TJSJ through
06/22Z, no impacts to operations expected. Winds from the ESE at 15-
20kts, with higher gusts, through 06/23Z when they are expected to
decrease. Winds will increase to similar values again after 07/13Z.

&&

.PREV DISCUSSION... /issued 432 AM AST Fri Jun 6 2025/

KEY MESSAGES...

* An elevated risk of flooding will persist over interior to
  western Puerto Rico due to afternoon showers and thunderstorms.
  Passing showers over the eastern region.

* Highs will range from the upper 80s to low 90s, with heat
  indices above 100 degrees.

* Winds will somewhat decrease into the weekend, remaining breezy
  in the afternoon for some coastal areas. Winds increasing again
  next week.

DISCUSSION...Today through Thursday...

During the overnight hours, mainly fair weather conditions prevailed
over the islands with mostly clear skies over the islands, with the
exception of western Puerto Rico earlier in the night as cloudy
skies prevailed in that area due to remnants of yesterday`s
afternoon convection. By 2 AM, almost all of this cloudiness was
over the Mona Passage. Shower activity was relegated to passing
showers mostly over the waters and steered by easterly winds. Since
midnight, radar estimated accumulations over land were found mostly
over the southeastern quadrant of Puerto Rico. Lows were at to below
in the upper normal over several areas, several official and
unofficial stations reported temperatures and in the low to mid 60s
over interior PR, in the low to mid 70s over western, north-central
and eastern interior PR and in the upper 70s to around 80 over other
lower elevation and coastal areas of Puerto Rico and the U.S. Virgin
Islands.

A mid level ridge and the presence of Saharan dust over the region
will persist into the weekend and early next workweek. A surface high
over the Atlantic will gradually strengthen during the period,
maintaining easterly, to east-southeasterly this weekend onwards,
steering flow. This surface high is also helping steer smoke from
wildfires at Canada over the local islands, deteriorating air
quality. Precipitable water values are expected to be generally at
below normal values, as a patch of drier air approaches the region
through Saturday afternoon. More humid air is forecast to arrive by
Saturday evening, maintaining PWAT values up to around 1.8 to 1.9
in for the rest of the period. A tropical wave will move across
the eastern Caribbean around Tuesday. This is due to the mid level
ridge starting to weaken and and moisture pulling into the area
due to the east- southeast steering flow and increasing the
diurnal pattern, although model uncertainty remains. Although a
decrease in wind speeds are forecast during the next couple of
days, up to breezy conditions are forecast, next week. The diurnal
pattern will persist during the period with showers over windward
sectors, especially in the morning, and afternoon showers and
thunderstorms over interior to western Puerto Rico, due to diurnal
heating, sea breeze convergence and topographic effects, and
downwind of El Yunque and the local islands. An elevated risk of
flooding is forecast over interior to western Puerto Rico each
afternoon. The trade winds will also continue to bring patches of
clouds and showers from time to time. Highs will reach the upper
80s to low 90s, with heat indices over 100 degrees. A limited heat
risk will persist for most coastal and lower elevation areas.

AVIATION...

(06Z TAFS)

Mainly VFR conditions expected. SHRA will move across the local
waters, reaching the VCTY of TIST, TISX, TJSJ & TJPS with little
impacts. SHRA and TSRA expected over interior to western PR after
around 06/17Z, with mountain obscuration over the interior.
Reduced visibilities and low ceilings possible for TJBQ. Winds
mainly from the E at 13-18kts with higher gusts after around
06/13Z.

MARINE...

A surface high pressure across the central Atlantic will continue
to promote moderate to locally fresh trade winds, shifting east
to southeast in the weekend. Isolated thunderstorms are expected
to develop each afternoon over the western waters of Puerto Rico.
A tropical wave will move across the eastern Caribbean around
Tuesday.

BEACH FORECAST...

The risk for rip currents is low today and tonight, however,
life-threatening rip currents often occur in the vicinity of
groins, jetties, reefs, and piers. By tomorrow evening, a moderate
risk of rip currents will be present for northern Puerto Rico,
Culebra and St. Croix. This moderate risk of rip currents will
possibly spread to the northern USVI and Vieques on Sunday and
southeastern Puerto Rico on Monday.

&&

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

$$

SHORT TERM...MNG
LONG TERM...CVB/MRR
AVIATION...CVB