textproduct: San Juan

KEY MESSAGES

Issued at 342 AM AST Fri Aug 28 2026

* Extreme Heat Remains the Main Hazard Today: Dangerous heat indices are expected, especially from late morning through the afternoon. A Heat Advisory is in effect for areas where hazardous heat conditions are expected.

* Afternoon Showers and Thunderstorms: Increasing moisture combined with daytime heating and local effects will promote showers and thunderstorms, particularly across interior and western Puerto Rico. Ponding of water and localized urban and small-stream flooding are possible.

* Tropical Wave Tonight into Saturday: A fast-moving tropical wave will increase passing showers and isolated thunderstorms late tonight into Saturday morning. Locally heavier rainfall may affect eastern Puerto Rico, but the wave's quick movement should limit the overall flooding threat.

* Monitoring Tropical Storm Dolly: Dolly is forecast to weaken as it approaches the eastern Caribbean. Moisture associated with Dolly and its eventual remnants could begin reaching the region late Saturday night into Sunday, followed by a potentially wetter pattern early next week. Forecast uncertainty remains higher than usual, so continue monitoring updates.

* Moderate Rip Current Risk: A moderate risk of life-threatening rip currents will continue along the northern and eastern exposed beaches of Puerto Rico and the U.S. Virgin Islands during the next several days. Beachgoers should exercise caution and remain alert for changes associated with swell action created by Dolly between Sunday and Monday.

Short Term(Today through Sunday)

Issued at 342 AM AST Fri Aug 28 2026

Overnight, patches of low-level moisture embedded in the easterly flow supported isolated to scattered showers across the local waters, with some reaching the U.S. Virgin Islands and windward portions of Puerto Rico. Rainfall accumulations were generally minimal, while leeward Puerto Rico experienced mostly clear skies and little to no rainfall. Winds were mainly from the east to east-southeast at 10 mph or less, with local land-breeze influences. Meanwhile, anomalously warm surrounding waters continue to support above-normal temperatures, with overnight readings generally in the upper 70s to lower 80s across coastal areas and locally remaining in the mid-80s.

Today, a mid-level ridge will continue to promote generally stable conditions. Nevertheless, patches of trade-wind moisture will support brief passing showers across the USVI and windward portions of PR through the morning. Extreme heat remains the primary hazard, with heat indices generally ranging from 100 to 111 degrees Fahrenheit, and locally higher, particularly between 10 AM and 5 PM AST. Therefore, a Heat Advisory is in effect for areas where hazardous heat conditions are expected.

By late morning into the afternoon, another patch of moisture moving within the east-southeast flow will combine with strong daytime heating, sea-breeze convergence, and orographic effects to promote increasing shower and thunderstorm development. The strongest activity should concentrate across the interior and western sections of PR, while brief passing showers remain possible across the USVI and windward portions of PR. Periods of moderate to locally heavy rainfall could cause ponding on roads and in poorly drained areas, with urban and small-stream flooding possible where the heaviest rainfall persists.

Late tonight into Saturday morning, a weak tropical wave will cross the region, bringing more moisture and supporting passing showers and isolated thunderstorms. Its relatively fast movement should limit the overall flooding threat; however, low-level convergence and orographic enhancement could produce locally heavier rainfall across eastern PR, where a limited flooding risk will persist. Brief downpours are also possible across the USVI. The wave will quickly move westward Saturday morning, followed by a noticeably drier air mass and increasing mid-level subsidence through Saturday afternoon and evening. Despite the drying trend, sufficient moisture combined with local effects may still support afternoon convection, particularly across western PR.

Attention then turns to Tropical Storm Dolly well east of the Lesser Antilles. Based on the latest National Hurricane Center track and intensity forecast, Dolly is expected to weaken while approaching the eastern Caribbean. Regardless of its eventual intensity, the leading edge of the tropical moisture associated with Dolly's remnants could begin reaching the area as early as late Saturday night, with a more substantial increase expected on Sunday. This moisture should increase the potential for showers and thunderstorms across PR and the USVI and may provide some short-term relief from the ongoing rainfall deficits. The latest U.S. Drought Monitor indicates that drought continues to expand and intensify across PR, with increasing impacts to streamflows, agriculture, reservoirs, and aquifers. At the same time, Extreme Drought (D3) remains entrenched across the U.S. Virgin Islands.

Long Term(Monday through Friday)

Issued at 342 AM AST Fri Aug 28 2026

Higher-than-normal forecast uncertainty persists into the beginning of the long-term period, primarily due to the evolution of Tropical Storm Dolly and its associated moisture field. The latest National Hurricane Center forecast indicates that Dolly should continue moving quickly westward while weakening, potentially degenerating into a remnant low before reaching the local islands as it encounters increasingly unfavorable environmental conditions. Nevertheless, Dolly and its associated moisture will continue to be closely monitored for potential impacts across the region.

A wetter pattern is favored Monday and possibly Tuesday as moisture associated with Dolly's remnants moves across or near the local area. This should support increased shower and thunderstorm activity, with a more widespread risk of limited flooding. Steering flow should favor passing showers across windward areas, followed by afternoon convection mainly across the interior and western to northwestern portions of Puerto Rico. Locally heavier rainfall will ultimately depend on Dolly's track and structure.

Forecast confidence decreases regarding the timing and magnitude of the moisture increase. Both the GFS and ECMWF generally indicate above-normal precipitable water values from the beginning of the workweek through at least Tuesday. However, the GFS remains wetter and more aggressive in its moisture field, while the ECMWF shows stronger ridging near the region that could disrupt the system and limit the northward extent of deeper moisture. Therefore, rainfall forecasts remain subject to change as Dolly's evolution becomes better defined.

Moisture should gradually decrease by late Tuesday as guidance indicates low to moderate concentrations of Saharan dust reaching the local islands. Nevertheless, precipitable water values are forecast to remain above normal through midweek before becoming more seasonable thereafter. Lingering moisture associated with Dolly's remnants should then be followed by another tropical wave passing mainly south of the region Wednesday night into Thursday. Additional moisture is expected on Friday. These features should maintain periods of passing showers across windward areas, with afternoon convection developing over Puerto Rico under a generally east-southeast steering flow.

The increased cloud cover and rainfall expected Monday should help limit the heat threat, with a more limited risk of excessive heat currently anticipated. However, elevated to potentially significant heat risks may return during much of the remainder of the long-term period, particularly during intervals of reduced cloud cover and rainfall.

Given the higher-than-normal uncertainty surrounding Dolly's evolution, continue to monitor the latest advisories from the National Hurricane Center and subsequent local forecasts for updates.

AVIATION

(06Z TAFS) Issued at 342 AM AST Fri Aug 28 2026

VFR conditions are expected to prevail across all terminals through the forecast period. Brief SHRA may affect TJSJ/TIST/TISX through the morning, but significant operational impacts are not anticipated. After 28/16Z, SHRA/isolated TSRA are expected to develop across interior and western PR, potentially resulting in brief MVFR or lower conditions at TJBQ and vicinity. Winds will increase from the E-ESE at 10-15 kt after 28/13Z, with sea-breeze variations and locally higher gusts near SHRA/TSRA.

MARINE

Issued at 342 AM AST Fri Aug 28 2026

Moderate to locally fresh trades are expected to prevail across the northeastern Caribbean for the rest of the week. A weak tropical wave will bring increased showers and isolated thunderstorms by early Saturday. Following this, Tropical Storm Dolly, currently over the central Tropical Atlantic, is expected to weaken into a strong tropical wave as it approaches the local area from Sunday into Monday. This will result in squally weather, strong gusts, and higher seas across most local waters. Small craft advisories may be issued as early as Saturday for the Atlantic offshore waters and the Anegada Passage.

BEACH FORECAST

Issued at 342 AM AST Fri Aug 28 2026

A moderate risk of rip currents will continue along the east and north facing beaches of Puerto Rico and the U.S. Virgin Islands through Saturday. Beachgoers must exercise caution, as life- threatening rip currents are possible along the surf zone. For Sunday and Monday, swells from Tropical Storm Dolly, will increase the risk to high, inexperienced surfers and beachgoers are urged to remain out of the water. In addition, thunderstorms with cloud to ground lightning and gusty winds are expected during this period.

FIRE WEATHER

Issued at 342 AM AST Fri Aug 28 2026

A generally stable pattern will prevail today under a mid-level ridge. Although dry fuels remain across portions of the islands due to the ongoing rainfall deficits, patches of trade-wind moisture will maintain relative humidity above critical thresholds. East to east-southeast winds around 10-15 mph are expected, with locally higher gusts. Afternoon showers and isolated thunderstorms will favor the interior and western portions of Puerto Rico, providing localized wetting rainfall. Therefore, critical fire-weather conditions are not anticipated today.

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.