textproduct: San Juan

KEY MESSAGES

Issued at 241 PM AST Mon Aug 31 2026

* Unsettled Weather: Periods of showers and thunderstorms will affect Puerto Rico and the U.S. Virgin Islands. Heavy rainfall could cause ponding and localized flooding in urban areas and small streams.

* High Rip Current Risk: Life-threatening rip currents will remain likely along north-and east-facing beaches of Puerto Rico and the U.S. Virgin Islands through this evening.

* Increasing Heat: Abundant moisture combined with hot temperatures will result in an elevated to high risk of extreme heat, particularly Tuesday and Wednesday.

* Beneficial rainfall ahead: Another tropical wave will increase rainfall chances during the second half of the workweek. Additional moisture early next week could bring further beneficial rainfall to the region.

Short Term(This evening through Wednesday)

Issued at 241 PM AST Mon Aug 31 2026

The region was under a southeasterly wind flow today. Weather stations along the windward sections reported prevailing winds from the east to east-southeast at 15 to 25 mph, with a station at Buck Island, St Thomas reporting sustained winds of 20 to 30 mph with higher gusts. Maximum temperatures ranged from the upper 80s to the low 90s across urban and coastal areas, with lower temperatures in the mountains and valleys. Skies were mostly cloudy along the eastern half of Puerto Rico and the US Virgin Islands, while the western half of Puerto Rico observed mostly sunny to partly cloudy skies. Thunderstorms developed along the northwest quadrant early this afternoon. Some showers moved across the US Virgin Islands and eastern PR from the east early this afternoon. A record maximum temperatures of 94 degrees Fahrenheit was tied at the San Juan Metropolitan area this afternoon.

An unstable weather pattern, fueled by abundant tropical moisture from the trailing remnants of Dolly, will keep the chance of showers and thunderstorms high across the region through at least tomorrow, Tuesday. Thus, we expect brief periods of unsettled weather for the US Virgin Islands and Puerto Rico through tomorrow, with a limited to elevated risk of flooding, meaning ponding in poorly drained areas and urban and small-stream flooding is likely, without ruling out isolated flash flooding, especially along the northwest quadrant of PR this afternoon. Later this evening into the overnight, we expect additional periods of showers and possibly isolated thunderstorms moving from the waters into the USVI and eastern PR. Then, by Tuesday afternoon, another round of convection is expected along the interior and western PR, as well as downwind of the Luquillo mountain range and downwind of St. Croix and St. Thomas.

A similar pattern is possible for Wednesday, but more seasonal, as most trailing moisture will exit the region. However, available moisture combined with local air temperatures will produce hot and possibly dangerous heat indices. Afternoon convection will form once again on Wednesday afternoon.

Long Term(Thursday through next Sunday)

Issued at 333 AM AST Mon Aug 31 2026

A surface high pressure system over the western Atlantic, interacting with another high over the central Atlantic, will remain the dominant surface feature through the first part of the long-term period. This setup will maintain an easterly wind flow across the region from Thursday into Friday, some pockets of moisture embedded in the easterly winds will move in and out of the forecast area. Under this pattern, variable weather conditions are expected, with periods of passing showers alternating with warm conditions and peak heat indices ranging from 100 to 111 degrees. In the afternoon, sea breeze convergence and local effects will combine with available moisture to promote convective development across western sectors of Puerto Rico, resulting in localized showers with a none-to-limited flooding threat across western sections of the island.

On Friday, surface conditions will change as the central Atlantic high expands southward into the Caribbean, inducing a south- southeasterly wind flow that will drag moisture from an approaching tropical wave into the forecast region. At the upper levels, a low pressure system will increase instability across the area, particularly during the late afternoon and evening hours. This evolving pattern will boost precipitable water (PWAT) values up to 2.0 inches, tighten the local pressure gradient to increase surface winds, and enhance cloudiness and shower potential across the region. According to the GFS, moisture will arrive early Friday morning and persist throughout the day; conversely, the ECMWF shows a more northerly moisture trajectory. Nevertheless, both global models agree on a similar outcome: an unstable and wet weather regime for the end of the workweek. By Saturday, low-level winds will remain from the southeast with sufficient low-level moisture in place. However, a upper-level southerly wind flow will filter mid- to upper-level clouds across the local islands for much of the day. This persistent cloud cover may limit surface insolation and slightly cap peak heat indices, though ambient temperatures will still ramp up into the upper 80s to low 90s, maintaining warm conditions and potential heat-related risks across lower elevations.

During the latter part of the long-term period from Sunday into Monday, atmospheric moisture will increase further as another tropical wave, lifting northward out of the Intertropical Convergence Zone (ITCZ), tracks into the local forecast area. Guidance suggests that the northern axis of this wave will interact with the local island terrain and favorable low-level wind convergence, pulling deep tropical moisture into the CWA and pushing precipitable water (PWAT) values above seasonal normals. This moisture increase will enhance cloudiness across the regional waters and islands, resulting in widespread passing showers over coastal areas during the overnight and morning hours. By the afternoon, the combination of daytime heating, local effects, and sea breeze convergence will significantly increase the potential for moderate to heavy shower and thunderstorm activity across interior and western sectors of Puerto Rico.

AVIATION

(18Z TAFS) Issued at 241 PM AST Mon Aug 31 2026

Moisture trailing the remnants of Dolly, mainly well west of the region, will continue to support SHRA and TSRA and mid to upper level cloudiness across the region thru the forecast prd. VCTS/TSRA most likely to affect TJBQ/TJSJ thru around 31/21Z, but remains psbl for other terminals. This TSRA can result in tempo MVFR/IFR conds. SHRA will remain psbl for the terminals thru much of the prd. E-ESE flow up to around 12 kt, with higher gusts, thru 31/23Z, decreasing overnight and picking up again from the E-ESE after 01/12Z.

MARINE

Issued at 241 PM AST Mon Aug 31 2026

Showers and thunderstorms associated with trailing moisture from the remnants of Dolly will continue to redevelop across the regional waters today. Periods of torrential rainfall, frequent lightning, and strong gusty winds are possible with the strongest thunderstorms. A Small Craft Advisory remains in effect for the offshore Atlantic waters, where seas could reach up to 7 feet. A weak surface high pressure building across the central Atlantic by midweek will promote moderate easterly trade winds through much of the workweek. The next tropical waves are forecast to reach the local waters toward the end of the workweek and early next week, bringing another increase in shower and thunderstorm activity.

BEACH FORECAST

Issued at 241 PM AST Mon Aug 31 2026

A high risk of life-threatening rip currents will persist along north- and east-facing beaches of Puerto Rico and the U.S. Virgin Islands through this evening. The risk is expected to decrease to moderate on Tuesday, then become low Wednesday and Thursday.

For St. Croix, the rip current risk should remain low through much of the workweek before increasing to moderate during the weekend.

Thunderstorms are also expected across the region. If you hear thunder, seek safe shelter immediately and stay away from the beach and open water.

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk until 6 PM AST this evening for PRZ001>003- 005-008-012-013.

VI...High Rip Current Risk until 6 PM AST this evening for VIZ001-002.

AM...Small Craft Advisory until 6 PM AST this evening for AMZ711.