textproduct: San Juan

KEY MESSAGES

Issued at 350 AM AST Tue May 12 2026

* Breezy to locally windy conditions will continue through at least the weekend as surface high pressure maintains a tight pressure gradient. Frequent passing showers will affect windward areas overnight and in the morning.

* Limited excessive rainfall impacts are expected Tuesday through Thursday, mainly across western Puerto Rico during the afternoon and eastern Puerto Rico/U.S. Virgin Islands overnight into the morning hours. Localized flooding and water ponding in poor drainage areas will remain possible.

* Heat risk will increase through the week and into the weekend as warmer-than- normal temperatures persist. Heat indices above 100F are likely across urban and coastal areas, with Heat Advisory conditions possible Thursday through the weekend.

* A generally stable pattern will limit widespread thunderstorm activity through most of the period, although we cannot rule out isolated thunderstorms each afternoon across interior and western Puerto Rico. A slightly wetter and more unstable pattern may develop by late weekend into early next week.

* Moderate to fresh easterly winds and a weak northeasterly swell will maintain choppy marine conditions and a moderate risk of rip currents through the period. Small craft should exercise caution, and life- threatening rip currents are possible for most north- and east- facing beaches of Puerto Rico, Vieques, Culebra, and the U.S. Virgin Islands.

Short Term(Today through Thursday)

Issued at 350 AM AST Tue May 12 2026

In general, tranquil weather conditions prevailed overnight. However, another wind surge brought a patch of moisture, promoting passing showers across the local waters, the US Virgin Islands, and Puerto Rico's windward locations. Low temperatures ranged from the mid-70s to the low-80s at urban and coastal sites, to the mid- and upper-60s at mountain sites. The winds were mainly from the east to east-southeast at 10 to 15 mph, with higher gusts across windward locations, and 5 to 10 across leeward sites, where land breeze fluctuations were also noted.

A surface high pressure will continue tightening the local pressure gradient, creating breezy to locally windy conditions across the region through at least the middle of the week. Under this wind pattern, pockets of low-level moisture embedded within the winds will be advected across the region, resulting in periods of showery weather, particularly during the overnight and early morning hours across windward areas.

A somewhat stable atmosphere is expected to continue due to a mid- to upper-level ridge, which is promoting subsidence aloft, limiting significant vertical development, and reducing the potential for widespread thunderstorm activity through the period. Nevertheless, local effects, strong diurnal heating, and sea breeze convergence will support afternoon convection each day across portions of eastern and interior Puerto Rico, as well as western Puerto Rico and parts of the U.S. Virgin Islands. Although we did not include thunderstorms in the forecast, we cannot rule out isolated thunderstorms, particularly given the excessive heating expected each afternoon.

We kept the limited flooding risk through the short term, especially across western Puerto Rico during the afternoon hours and across eastern Puerto Rico and the U.S. Virgin Islands during the evening and early morning hours.

Model guidance has been consistently indicating the potential for warm-to-hot heat indices each day. But even hotter around the middle of the week, when we continue evaluating the necessity of issuing a Heat Advisory, as above-normal temperatures continue to present. This trend will increase the risk of heat-related effects, primarily for individuals highly sensitive to heat, especially those outdoors without effective cooling and/or adequate hydration.

Long Term(Friday through Tuesday)

Issued at 350 AM AST Tue May 12 2026

Weather conditions over the upcoming weekend will remain mostly stable, becoming slightly unstable on Monday. A broad surface high pressure should linger over the Central Atlantic, promoting mainly southeasterly winds that will likely result in breezy to locally windy conditions across the islands. The high will drag and move patches of moisture into the region, with isolated showers moving over windward sections from time to time. Another surface high should build over the Western Atlantic, though the latest model guidance suggests that it should linger there through the long- term forecast instead of migrating eastward. The col region mentioned in the previous discussions should remain far north of the region, with winds remaining strong.

In the mid to upper levels, the ridge will continue to dominate the weather pattern throughout the weekend, with warmer-than- normal 500 mb temperatures (between -5 and -6 degrees Celsius), with low potential of deep convection. Although afternoon convection is expected on Friday and Saturday afternoon, it should remain shallow, with limited shower activity across western/northwestern Puerto Rico. Puddles over the road, reduced visibility, can be expected, though no significant flooding potential is expected.

The latest model guidance continues to suggest an upper-level trough that will deepen into the tropics, which may become a cut- off low near the Bahamas by late Sunday, with the CWA positioned under the favorable side of convection. Besides cooling mid-level temperatures (around -7 degrees Celsius), the proximity of the low should allow ventilation and cloud growth, increasing the potential of deeper convection. With low to mid level moisture content increasing, showers and isolated thunderstorms likelihood is increasing. Hence, from Sunday onwards, frequent passing showers are expected over windward sections of Puerto Rico and the U.S. Virgin Islands, particularly overnight into the morning hours, along with afternoon convection over interior and western/northwestern Puerto Rico. Additionally, streamers may develop over the waters and the San Juan Metropolitan Area. Taking in consideration local effects, diurnal heating, and sea breeze convergence, showers may persist and result in ponding of water over roadways and poorly drained areas, along with minor flooding.

Minor concentrations of SAL may persist during the weekend, with the highest concentrations remaining south of the CWA according to the latest NASA DUex product. Nevertheless, residents and visitors should take necessary precautions if sensitive to these particles.

As for temperatures, model guidance suggests warmer-to-hotter conditions this weekend, with 925 mb temperatures well above normal. If winds remain with a southerly component, with the available moisture, urban and coastal areas will very likely experience heat indices above 100 degrees Fahrenheit, localized areas reaching Heat Advisory Criteria. Hence, the heat risk will remain elevated this weekend, stay hydrated and avoid long sun exposure.

AVIATION

(06Z TAFS) Issued at 350 AM AST Tue May 12 2026

Mainly VFR conditions will prevail with fast-moving SHRA/-SHRA arriving due to the breezy E-ESE winds. SHRA/+SHRA will form across the interior and northwest PR between 12/17-23z, probably affecting JBQ, which could promote brief MVFR or brief IFR conds. Winds will prevail from the E-ESE at 5-15 kt with higher gusts, then after 12/13z winds will range between 15-20kt with higher gusts and sea breeze variations.

MARINE

Issued at 350 AM AST Tue May 12 2026

The surface high pressure over the western Atlantic will be replaced by a low pressure system over the central Atlantic. Expect the moderate to locally fresh east to southeast winds to prevail across the regional waters, before gradually weakening after midweek. Seas are expected to range between 3 to 5 feet with occasional wave heights reaching up to 6 feet. Choppy seas are expected to prevail across the local waters.

BEACH FORECAST

Issued at 350 AM AST Tue May 12 2026

Breezy to locally windy conditions will continue across the region through at least midweek, maintaining a moderate risk of rip currents along most local beaches, particularly along north- and east-facing coastlines.

A weak long-period northeasterly swell is also expected to arrive across the Atlantic beaches by midweek, which could further increase the risk of dangerous rip currents. Beach visitors are urged to swim only at beaches with lifeguards on duty, remain aware of surf conditions, and avoid venturing too far from shore.

SJU WATCHES/WARNINGS/ADVISORIES

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