textproduct: San Juan

KEY MESSAGES

Issued at 258 PM AST Tue Sep 1 2026

* Afternoon showers and thunderstorms will result in periods of moderate to heavy rain, which could cause ponding and localized flooding in urban areas and small streams, especially across Puerto Rico's western half. The US Virgin Islands will see passing showers.

* Moderate Rip Current Risk: Life-threatening rip currents will be possible along the north and east 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 tomorrow, Wednesday.

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

Short Term(This evening through Thursday)

Issued at 258 PM AST Tue Sep 1 2026

Mostly calm weather prevailed in the morning, with maximum temperatures in the upper 80s and low 90s and variable cloudy skies, as we observed mostly cloudy skies across portions of the USVI and eastern and western PR in the morning, with clear skies along the interior and southern portions of PR. Later in the day, a line of showers developed downwind from St Croix, affecting the western parts and surrounding waters. Winds were mainly from the east to east-southeast at 5 to 15 mph with sea breeze variations.

An upper-level trough will continue to increase local instability across the northeast Caribbean. In addition, plenty of tropical moisture will continue across the region through at least Thursday. These features will continue to produce periods of heavy showers and isolated strong thunderstorms each afternoon and evening. Then, low-level convergence, enhanced by east- southeast winds and local topography, will promote periods of showers across the windward locations of the USVI and PR each day. This weather pattern will continue to result in a limited to elevated risk of flooding this afternoon and Wednesday.

Above-normal temperatures will continue across the region. As a result, heat products associated with extreme heat may be needed for Wednesday afternoon, especially in areas without rain.

Thursday, the driest day of the short-term forecast (at this moment), will feature warm to hot temperatures with little or no rain. This rain will mainly come from patches of moisture embedded in the winds affecting the windward locations, followed by afternoon convection across western PR and downwind from the USVI.

Long Term(Friday through Tuesday)

Issued at 434 AM AST Tue Sep 1 2026

A surface high pressure extending from the central Atlantic into the western Atlantic and two tropical waves will be the main weather features during the long-term period. From Friday into Saturday, the surface high pressure will maintain generally moderate easterly winds across the region. Aloft, an upper-level low will remain nearby, resulting in periods of upper-level cloudiness, while a mid- level ridge near 500 mb should provide some stability. This stable pattern is also reflected in the relatively warm 500-mb temperatures, forecast to remain near -4C. These conditions should limit widespread shower development; however, the available moisture combined with local effects may enhance some afternoon convection across western Puerto Rico, particularly in the vicinity of Mayaguez. No significant rainfall threat is anticipated with this activity. The main concern will continue to be excessive heat, with warm temperatures and heat indices potentially reaching around 111F. This is also supported by 925-mb temperatures forecast to remain around two standard deviations above normal. These conditions will support above-normal temperatures and maintain the potential for elevated heat indices across Puerto Rico and the U.S. Virgin Islands, where Heat Advisories may be required. By late Friday into Saturday, precipitable water values are expected to increase as a weak tropical wave moves across the islands, with PWAT values rising to around 1.8 inches. This feature will provide additional moisture for passing showers, although the overall influence of the mid-level ridge should limit widespread organized convection. Meanwhile, southerly winds around 250 mb will begin to develop as the upper- level pattern gradually evolves.

Conditions are expected to become more unsettled from Sunday into Monday as a better-defined tropical wave, accompanied by deeper mid- level moisture, moves across the region, resulting in a more favorable environment for shower and thunderstorm development. Based on the latest guidance, the deepest moisture associated with this feature appears more likely to be displaced toward northern Puerto Rico and the Atlantic waters. Additionally, southeasterly flow at 250 mb, combined with an area of positive cyclonic vorticity around 850 mb, should provide additional dynamical support, particularly where the deeper moisture associated with the wave is present. Therefore, an increase in shower and thunderstorm activity can be expected during this period, with afternoon convection likely becoming more active across portions of Puerto Rico. By Tuesday, conditions should gradually begin to improve as the central Atlantic surface high strengthens and the low-level winds become more southeasterly across the local area. This evolving wind pattern should gradually push much of the available moisture northward into the Atlantic, allowing somewhat drier conditions to filter into the region.

AVIATION

(18Z TAFS) Issued at 258 PM AST Tue Sep 1 2026

Mainly VFR conditions will prevail. However, VCTS/-TSRA will continue to affect mainly TJSJ/TJBQ/TJPS thru around 01/21Z, prompting brief to Tempo MVFR conditions. -SHRA/Iso -TSRA will remain psbl for eastern and southern terminals thru much of the prd as E-ESE flow continues to steer them towards the region. E-ESE flow up to around 15 kt, with higher gusts and higher near TS, thru 01/23Z, decreasing overnight and picking up again from the E-ESE after 02/12Z with sea breeze variations and local effects. VCTS/- TSRA once again forecast at around 02/17Z and mainly affecting PR terminals.

MARINE

Issued at 258 PM AST Tue Sep 1 2026

A surface high pressure will continue to build over the far eastern Atlantic and promote moderate trades through 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. For the rest of today and this evening, lingering tropical moisture and a weak trough will continue to promote shower and thunderstorm activity across the regional waters.

BEACH FORECAST

Issued at 258 PM AST Tue Sep 1 2026

A moderate 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. Then, the moderate risk will be limited to the northwest and northcentral portion of PR.

The risk will turn low through at least next week. However, we encourage beachgoers to exercise caution as life-threatening rip currents may still occur, especially near groins, jetties, reefs, and piers. Always swim near a lifeguard and remember to heed the advice of the local beach patrol and flag warning systems.

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