textproduct: San Juan

KEY MESSAGES

Issued at 135 AM AST Thu Mar 12 2026

* Ponding of water is anticipated with the expected increase shower activity across Puerto Rico.

* Slightly drier trend by late Friday into Saturday, but showers may develop during the afternoon hours.

* Lighter winds are expected through early Saturday, increasing on Sunday, leading hazardous marine and beach conditions.

* Across the U.S. Virgin Islands, occasional passing trade wind showers will continue, with a drying trend expected by late Friday and Saturday.

Short Term(Today through Saturday)

Issued at 135 AM AST Thu Mar 12 2026

Overnight conditions were generally calm, with passing showers affecting portions of northern to northeastern Puerto Rico, Vieques, Culebra, and the U.S. Virgin Islands under partly cloudy skies. Rainfall accumulations were mostly light, generally between 0.10 and 0.30 inches, with localized accumulations reaching 0.50 inches over the Caribbean waters. Winds remained light and variable, increasing slightly in the heaviest shower activity. Temperatures stayed in the upper 60s to mid-70s along coastal areas and from the low to upper 60s across interior and mountainous areas.

Today into Friday will be the wettest days of the short-term period, before conditions gradually trend drier late Friday into the start of the weekend. The latest model guidance indicates precipitable water values between 1.50 and 1.75 inches through Friday, decreasing to around 1.20 inches by Saturday, which is near normal values for this time of year. The causes of this wet pattern will be an upper-level trough and an induced low-level trough, which will enhance shower activity and produce periods of moderate to heavy rainfall. The primary hazard will be urban and small-stream flooding, especially today, as weak steering winds will allow showers to move slowly, particularly across mountainous areas. Gusty winds may accompany the strongest activity. Meanwhile, 500 mb temperatures around 10 C would typically support some lightning potential; however, recent similar conditions have produced little to no lightning activity, so the probability of thunderstorms today remains low to near zero despite the abundant atmospheric moisture.

By late Friday into Saturday, drier air and more stable conditions will gradually spread across the region as precipitable water values return closer to seasonal levels, as a high pressure system build over the Atlantic. Nevertheless, trade wind showers will support afternoon showers, mainly across western Puerto Rico, as easterly winds will dominate the forecast area.

Long Term(Sunday through Thursday)

Issued at 135 AM AST Thu Mar 12 2026

A broad surface high will move into the western Atlantic and continue building, promoting increased E to ESE winds. 925 mb wind speeds will be above normal to briefly 2 standard deviations above normal, resulting in breezy to locally windy conditions to start the next week. Unsecured items could blow around. A limited wind risk will persist during the long term period with an elevated wind risk possible on Sunday and Monday. Although an upper trough will move northwest of the islands on Monday and an upper jet over the area can provide ventilation, 500 mb temperatures will be warmer compared to the short term period, at -7 to -6 degrees Celsius, while 700 to 500 mb lapse rates will be at below normal to low end normal values for this time of the year. This will promote more stable conditions and limit vertical shower development. However, the breezy to windy E to ESE flow will steer showers and patches of moisture towards windward sectors with diurnal heating promoting afternoon convective showers over interior to northwestern PR, as well as lines of showers towards the USVI, Vieques and Culebra to E and ESE PR. Patches of moisture arriving towards the islands will maintain precipitable water (PWAT) values around normal values (with some variability related to the moist and dry patches), model guidance suggests that the most broad moisture patch will arrive late Sunday into Monday. 925 mb temperatures will remain at normal values but under a general warming trend with less cloud cover and the E to ESE flow. Patchy fog during the overnight hours at sectors of the interior. Low concentrations of saharan dust will also be steered over the region, particularly on Sunday and Monday.

AVIATION

(06Z TAFS) Issued at 135 AM AST Thu Mar 12 2026

VFR conds will prevail across all TAF sites. VCSH possible at all terminals during the period. However, SHRA could cause periods of MVFR condt mainly by 12/17Z at TJSJ/TJBQ/TJPS. E-NE winds btwn 10-15 kt with gusts up to 20 kt and sea breeze variations aft 12/14Z.

MARINE

Issued at 135 AM AST Thu Mar 12 2026

A weakening of the pressure gradient across the northeastern Caribbean will result in lighter winds. Winds are expected to remain gentle to moderate, with seas decreasing to between 3 and 5 feet, resulting in improving marine conditions today and into the early part of the weekend. However, winds are forecast to begin increasing again around Saturday night into Sunday, leading to rough and choppy seas and likely prompting Small Craft Advisory conditions from late in the weekend into early next week, with seas building to around 6 to 8 feet.

BEACH FORECAST

Issued at 135 AM AST Thu Mar 12 2026

Today, winds are expected to subside, resulting in improved conditions. However, the rip current risk will remain moderate along north- and east-facing beaches of Puerto Rico, Culebra, and St. Croix, and low elsewhere. The same pattern will continue through early Sunday.

The risk is forecast to increase to high around Sunday night into early next week, along with breezy to windy conditions. Residents and visitors are encouraged to monitor the forecast for any updates or adjustments. For additional information and location-specific rip current details, please visit weather.gov/beach/sju.

FIRE WEATHER

Issued at 135 AM AST Thu Mar 12 2026

The risk for fire weather treats remains LOW today, as winds are expected to become light to moderate and RH values are expected increase due to the arrival of another patch of moisture across the area. At this time an RFD will not be issued, but we encourage partners to continue monitoring conditions in the coming days.

SJU WATCHES/WARNINGS/ADVISORIES

PR...None. VI...None. AM...None.