textproduct: San Juan

KEY MESSAGES

Issued at 226 PM AST Fri Aug 28 2026

* Extreme heat remains the primary hazard through Saturday, with some relief expected Sunday into Monday before hazardous heat returns around midweek.

* Wetter and windier conditions are expected Sunday into Monday as moisture associated with Dollys remnants moves across the region. Lingering moisture may continue into Tuesday.

* Flooding, lightning, and gusty winds will become the main hazards Sunday into Monday. Urban flooding is likely with the heaviest rainfall, with isolated flash flooding possible. Rainfall amounts and the location of the highest totals remain uncertain.

* Marine and coastal hazards will increase late this weekend into early next week as winds and seas build, increasing risks for small craft, rip currents, and breaking waves.

Short Term(This evening through Sunday)

Issued at 226 PM AST Fri Aug 28 2026

Tonight into Saturday, intermittent pockets of wetter and drier air will continue streaming across the region within the easterly flow. Passing showers will affect the USVI and windward portions of Puerto Rico tonight, and while thunderstorms are not explicitly expected, one or two isolated thunderstorms cannot be ruled out. A drier air mass will follow during the day Saturday, with heat remaining the primary hazard. Only minimal localized shower and thunderstorm development is expected during the afternoon.

Sunday will mark a transition toward increasingly unsettled and windy conditions. Winds will gradually strengthen through the day as deeper tropical moisture associated with the remnants of Dolly approaches the region, with showers and thunderstorms becoming progressively more frequent. Activity should first increase across the USVI Sunday morning, spread into Vieques, Culebra, and eastern Puerto Rico by late morning into early afternoon, and expand across Puerto Rico later in the day. With winds initially becoming northeasterly ahead of the approaching wave, afternoon shower and thunderstorm development should favor the southwestern quadrant of Puerto Rico. Locally heavy rainfall may produce urban and poor-drainage flooding, with isolated flash flooding possible where the heaviest rainfall persists. Lightning and gusty winds will also become increasingly important hazards.

Conditions will deteriorate further Sunday night as the wave and deepest tropical moisture move across the islands. Numerous showers and thunderstorms are expected, with the most persistent activity favoring the USVI, Vieques, Culebra, and eastern Puerto Rico. Periods of heavy rainfall will support an elevated excessive rainfall risk, with urban and poor-drainage flooding becoming increasingly likely and isolated flash flooding remaining possible. Lightning and gusty winds will remain additional hazards.

Long Term(Monday through next Thursday)

Issued at 226 PM 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

(18Z TAFS) Issued at 226 PM AST Fri Aug 28 2026

VFR conds are expected to prevail across most terminals thru the fcst period. VCSH will remain psbl at TJPS this aftn, while SHRA/iso TSRA across interior and W PR may briefly affect TJBQ and vicinity with MVFR or lower cigs/vsbys. A weak disturbance will bring passing SHRA overnight, mainly across TJSJ/TIST/TISX, with brief MVFR conds psbl. Conds should improve and become mostly VFR/drier after 29/13Z. E-ESE winds will peak at 15-20 kt thru around 28/23Z, diminish to 5-10 kt overnight, then increase again to 15-20 kt after 29/13Z.

MARINE

Issued at 226 PM AST Fri Aug 28 2026

A weak tropical wave will bring a gradual increase in showers and isolated thunderstorms by early Saturday. What used to be Tropical Storm Dolly is now a broad tropical wave, moving westerly across the central Tropical Atlantic, and reaching the islands 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 into Sunday for the Atlantic offshore waters and the Anegada Passage.

BEACH FORECAST

Issued at 226 PM AST Fri Aug 28 2026

The moderate risk of rip currents should 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. What used to be Tropical Storm Dolly is now a broad tropical wave and will deteriorate Sunday and Monday, swells from the system 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. Therefore, avoid unnecessary trips to the beach, particularly those along the east and northern coast of Puerto Rico and the US Virgin Islands.

HYDROLOGY

Issued at 226 PM AST Fri Aug 28 2026

The remnants of Tropical Storm Dolly will arrive into the area late on Sunday and Monday as a strong tropical wave. A widespread and long-lasting rainfall event is not anticipated at this time. Instead, areas of squally weather will bring periods of moderate to locally heavy rainfall. These rains are expected to be mostly beneficial due to the ongoing drought, but are not expected to be enough to end the severe to extreme drought conditions. While the risk of flooding will be low to locally moderate, some areas may experience flooding if the drainage system is clogged with dead vegetation debris or if it is in an area with poor drainage. Please refer to the latest Hydrologic Outlook, ESFSJU, for more details.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007- 008-010>013.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...None.