textproduct: San Juan

KEY MESSAGES

Issued at 339 AM AST Tue Jul 28 2026

* A hot weather pattern continues today. A Heat Advisory remains in effect for coastal and urban areas of Puerto Rico and the U.S. Virgin Islands, where dangerous heat indices are expected.

* A tropical wave will bring periods of showers and thunderstorms today. The U.S. Virgin Islands can expect passing showers moving inland, while the greatest coverage of thunderstorms is expected across the interior and western portions of Puerto Rico. Heavy rainfall may lead to localized urban and small- stream flooding.

* Drier weather returns from Wednesday afternoon onward. A drier air mass, accompanied by Saharan dust, will overspread Puerto Rico and the U.S. Virgin Islands through the end of the week, reducing rainfall coverage while maintaining hot and hazy conditions.

* Another tropical wave may approach the region late this weekend. While it could increase the potential for showers and thunderstorms, confidence in the timing and impacts remains low at this time.

* Increasing winds will promote a moderate risk of life- threatening rip currents along windward-facing beaches in Puerto Rico and the U.S. Virgin Islands over the next several days.

Short Term(Today through Thursday)

Issued at 339 AM AST Tue Jul 28 2026

Although the moisture field associated with a tropical wave persisted across the region overnight, with precipitable water (PWAT) values between 1.75 and 2.00 inches, increasing mid-level ridging over the northeastern Caribbean was sufficient to suppress widespread convection. As a result, skies remained mostly clear, with only a few passing showers over the local Atlantic and Caribbean waters and the windward locations. Another warmer-than- normal night was observed across Puerto Rico and the U.S. Virgin Islands, with minimum temperatures generally in the upper 70s to lower 80s across coastal and urban areas. Surface winds remained light to moderate from the east to east-southeast at 5 to 10 mph, accompanied by typical land-breeze variations.

Today, the lingering tropical moisture, combined with another warmer-than-normal day, will continue the dangerous heat pattern across Puerto Rico and the U.S. Virgin Islands. Consequently, a Heat Advisory remains in effect from 10 AM to 5 PM AST for coastal and urban areas, where heat indices are likely to reach hazardous levels, particularly in locations that receive little or no rainfall.

Throughout the morning, low-level convergence will support a few passing showers across the USVI and eastern PR. Local topographic effects will likely enhance shower development downwind of the U.S. Virgin Islands, Vieques, and the Luquillo Mountain Range, resulting in streamers capable of producing periods of moderate to locally heavy rainfall. By the afternoon, daytime heating, sea- breeze convergence, and orographic lifting are expected to promote scattered to numerous showers and thunderstorms across the interior and western portions of Puerto Rico. There is a medium to high probability that some thunderstorms will become strong, producing torrential rainfall, frequent lightning, gusty winds, without ruling out small hail (similar to activity observed on Monday). Therefore, an elevated risk of urban and small-stream flooding is expected, with isolated flash flooding possible where storms repeatedly affect the same locations. Residents and visitors should remain alert for rapidly changing weather conditions and the potential issuance of additional short-fused warnings or advisories.

By Wednesday, the trailing moisture associated with the tropical wave will gradually shift west of the area as a drier air mass accompanied by suspended Saharan dust overspreads the northeastern Caribbean. Nevertheless, sufficient low-level moisture and daytime instability will likely persist to support afternoon showers and isolated thunderstorms, mainly across the interior and western portions of Puerto Rico, where local effects will remain favorable for convection. Dangerous heat conditions are expected to continue across coastal and urban areas, particularly where rainfall is limited. Model guidance indicates precipitable water values decreasing to around 1.15 to 1.45 inches by Wednesday night and Thursday, supporting a lower probability of widespread convection. Periodic pulses of Saharan dust will also promote hazier skies through the latter part of the week while limiting shower coverage mainly to passing trade-wind showers and localized afternoon convection over western Puerto Rico.

Long Term(Friday through Tuesday)

Issued at 339 AM AST Tue Jul 28 2026

A variable weather pattern may be expected in the long-term forecast. A surface high pressure over the Central Atlantic will dominate most of the wind pattern, mainly from the ESE-SE through most of the period, though it may become from the northeast by late Monday night. Although conditions will remain breezy during the upcoming weekend, winds may weaken by the end of the period.

Based on the latest model guidance, patches of moisture may arrive by Friday morning, with isolated showers moving across the regional waters and windward sections of the islands, followed by afternoon convection over portions of northwestern Puerto Rico. Although the latest model solution suggests an increase in low- and mid-level moisture, lingering Saharan dust concentrations and strong winds may not lead to significant flooding or lightning threat. A similar weather pattern may repeat on Saturday, though a drier slot may move across the CWA by the afternoon along with ridging in the mid-levels that should limit shower activity and lower flooding risk.

The weather pattern on Sunday and Monday may become slightly unstable as a tropical wave and an upper-level low approach the local area, introducing tropical moisture and instability across the CWA. The latest global model solutions suggest an increase in both low- to mid-level moisture (above 60 - 70%), cool mid-level temperatures (500 mb temperatures between -6 and -7 degrees Celsius), and enhanced lifting promoting cloud growth and introducing instability, though they differ with timing. While the latest deterministic guidance of the GFS suggests the bulk of moisture arriving on Sunday afternoon into the evening, the ECMWF delays the tropical wave until Monday morning. Although both models position the upper-level low over Hispaniola early Monday and suggest an increase in shower and thunderstorm activity, this introduces uncertainty to the forecast. Another factor that introduces uncertainty to the forecast is another plume of Saharan dust accompanying the tropical wave, which may weaken it by the time it moves across the area. Hence, the flooding threat will remain limited for both days, particularly over western/northwestern Puerto Rico due to the combination of available moisture, daytime heating, and local effects.

Under an ESE-SE wind flow, warmer to hotter temperatures can be expected across the CWA, particularly over urban and low-lying areas. With the available moisture content, heat indices will likely exceed 100 degrees Fahrenheit and affect most individuals, particularly those without adequate hydration or effective cooling. Therefore, the heat threat will remain elevated throughout the forecast period; Heat Advisories may be issued if required.

AVIATION

(06Z TAFS) Issued at 339 AM AST Tue Jul 28 2026

VFR conds will prevail through much of the period. Passing SHRA may bring brief MVFR cigs/vsbys to TIST/TISX and TJSJ after 28/10Z. SHRA/TSRA will increase after 28/16Z, with TEMPO MVFR/IFR conds likely at TJBQ and possible at TJSJ due to +SHRA/TSRA, reduced vsbys, mtn obscurations, and gusty outflow winds. ESE sfc winds 10-15 kt with gusts up to 25 kt, becoming light/vrb after 28/23Z. Stronger TSRA may produce gusts above 30 kt and frequent lightning.

MARINE

Issued at 339 AM AST Tue Jul 28 2026

Abundant moisture associated with a passing tropical wave will increase the potential for showers and thunderstorms through this evening. Gentle to moderate east to east-southeast winds will continue today across the region, becoming moderate to fresh by later this afternoon into Wednesday as high pressure system continues to strengthens over the Atlantic, tightening the pressure gradient. These winds will maintain choppy seas across portions of the Atlantic waters, offshore Caribbean waters, and the local passages, with seas up to 6 feet expected in localized areas from midweek through the weekend.

BEACH FORECAST

Issued at 339 AM AST Tue Jul 28 2026

A moderate risk of rip currents is forecast across northern Puerto Rico today. However, a low risk of rip currents is expected to continue elsewhere as gentle to moderate winds continues to prevail today. Caution is always recommended, as even when the risk is low, life-threatening rip currents can occur near reefs, jetties, groins, and piers. From this afternoon onwards, winds will continue to increase as high pressure over the Atlantic strengthens from Wednesday onwards, becoming breezy to locally windy. As a result, the moderate risk of rip currents will expand to most beaches of Puerto Rico and the U.S. Virgin Islands. Life-threatening rip currents will remain possible, exercise caution.

Additionally, warm to hot conditions will prevail, mainly across coastal and low-elevation areas. Stay hydrated and take frequent breaks in the shade. Beachgoers should also remain alert for thunderstorms.

FIRE WEATHER

Issued at 339 AM AST Tue Jul 28 2026

Although increasing tropical moisture will keep minimum relative humidity above critical thresholds in the short term, critically dry fuels persist across southern Puerto Rico and St. Croix, with Keetch-Byram Drought Index (KBDI) values remaining above critical thresholds. At the same time, easterly winds are expected to gradually increase during the next couple of days, which could promote the spread of any fire that develops. Residents and visitors should avoid outdoor burning and exercise caution with activities that could generate sparks or open flames, particularly across areas with critically dry vegetation.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for PRZ001>005-007-008-010>013.

VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for VIZ001-002.

AM...None.