textproduct: San Juan

KEY MESSAGES

Issued at 353 AM AST Wed May 13 2026

* Breezy to locally windy east to east-southeasterly winds will persist through the forecast period as high pressure over the western Atlantic maintains a tight local pressure gradient. * Heat risk will increase from late week into the weekend as warmer-than-normal temperatures combine with above-normal sea surface temperatures and available moisture. Heat indices above 100F are likely across urban and coastal areas, and Heat Advisories may become necessary for the USVI and PR.

* A generally stable weather pattern will limit widespread thunderstorm activity through the weekend. However, overnight and morning showers will pass across windward areas in PR and the USVI, followed by afternoon convection across interior and western PR each day. Localized ponding of water and minor flooding remain possible.

* A more unstable and wetter pattern may develop early next week as an upper-level trough approaches the region, increasing the potential for more frequent showers and isolated thunderstorms.

* Moderate rip current risk will continue along many local beaches, especially along north- and east-facing coastlines. A long-period northeasterly swell late this week could promote life- threatening rip currents, especially on Thursday.

Short Term(Today through Friday)

Issued at 353 AM AST Wed May 13 2026

A surge of moisture brought fast-moving showers across the local waters, the USVI, and south and east PR, moving further inland under the east-southeast winds. Low temperatures ranged from the mid-70s to the low-80s at urban and coastal sites, to the mid- and upper-60s at mountain sites. The winds were mainly from the east to east-southeast at 10 to 15 mph, with higher gusts across windward locations, and 5 to 10 across leeward sites, where land breeze fluctuations were also noted.

The local pressure gradient will continue to promote an east- southeasterly wind flow across Puerto Rico and the U.S. Virgin Islands today, and likely through at least tomorrow. Winds are likely to turn more easterly by Friday. In addition, sea surface temperatures across the surrounding Atlantic and Caribbean waters remain above normal. This pattern, combined with the available low-level moisture, will continue to support above-normal heat indices across urban and coastal areas during the peak heating hours each day, generally between 9 AM and 3 PM AST.

Model guidance continues to indicate a warming trend, particularly by Thursday and Friday. If widespread, prolonged rainfall does not materialize, an elevated risk of extreme heat may develop across portions of the area. This level of heat could affect most heat-sensitive individuals, especially those without effective cooling or adequate hydration. It could also increase stress on heat-sensitive industries and some healthcare systems.

At the mid to upper levels, a ridge pattern will continue to promote subsidence and dry air aloft, limiting significant vertical development and reducing the potential for widespread thunderstorm activity. However, patches of low-level moisture moving within the trade wind flow, combined with local effects and low-level convergence, will continue to produce periods of showery weather across windward sections of Puerto Rico and the U.S. Virgin Islands, particularly during the overnight and early morning hours. Afternoon convection driven by sea breeze convergence and daytime heating is then expected each day across interior and western Puerto Rico. As a result, a limited flooding risk will persist each day, mainly in areas with poor drainage and localized ponding.

Additionally, model guidance continues to suggest the arrival of trace concentrations of Saharan dust particles across the region from Friday into the weekend. At this time, concentrations are expected to remain relatively low, with only minor impacts to visibility and air quality anticipated.

Long Term(Saturday through Wednesday)

Issued at 353 AM AST Wed May 13 2026

A drier to seasonal weather pattern is anticipated over the long- term forecast. A surface high pressure building over the Western Atlantic should maintain E-SE winds throughout the period, promoting breezy to locally windy conditions across the islands. The mid-level ridge should keep dominating the weather pattern on Saturday and Sunday, bringing subsidence and promoting stability aloft. Nevertheless, as mentioned in the previous discussion, an upper- level trough will likely extend into the tropics and is likely to become a cut-off low over the Bahamas by Tuesday. From the latest model guidance, 250 mb heights star to drop Sunday onwards, with 500 mb temperatures cooling (around - 7 degrees Celsius). Additionally, PWAT values will likely increase up to 1.75 inches (typical for this time of the year), with a low chance of reaching 2.0 inches. The most likely scenario is to expect shower activity each day, with afternoon shallow convection across western/northwestern Puerto Rico on Saturday and Sunday. Although no flooding impacts are expected, expect puddles over the road, slippery pavement, and reduced visibility. On Monday onwards, the frequency of showers will increase and may produce minor flooding over windward sections, with afternoon showers and isolated thunderstorms over western and northwestern Puerto Rico, including the San Juan Metropolitan Area. Hence, the flooding threat will remain limited over the aforementioned areas for the rest of the forecast period.

As southeasterly winds will prevail, warmer-than-normal temperatures and the available moisture will result in heat indexes exceeding 100 degrees Fahrenheit, with a limited to elevated heat risk. Residents and visitors should stay tuned to further updates, as Heat Advisory issuances cannot be ruled out.

Minor concentrations of SAL will linger through the weekend, according to the latest NASA DUex. Although the highest concentrations should remain well south of the region, individuals sensitive to these particles should exercise caution.

AVIATION

(06Z TAFS) Issued at 353 AM AST Wed May 13 2026

Mainly VFR conditions will prevail with fast-moving SHRA/-SHRA arriving due to the breezy E-ESE winds. Additional SHRA/+SHRA will form across the interior and northwest PR between 13/16-23z, probably affecting JBQ and JPS, which could promote brief MVFR or brief IFR conds. Winds will prevail from the E-ESE at 5-15 kt with higher gusts, then after 13/13z winds will range between 15-20kt with higher gusts and sea breeze variations.

MARINE

Issued at 353 AM AST Wed May 13 2026

A broad surface high pressure over the central to western Atlantic will gradually be replaced by a low pressure system over the central Atlantic. Expect the moderate to locally fresh east to southeast winds to prevail across the regional waters, before gradually weakening after midweek. Seas are expected to range between 3 to 5 feet with occasional wave heights reaching up to 6 feet. Choppy seas are expected to prevail across the local waters.

BEACH FORECAST

Issued at 353 AM AST Wed May 13 2026

The breezy to locally windy conditions will continue across the region through at least midweek, maintaining a moderate risk of rip currents along most local beaches, particularly along north and east-facing coastlines. A long-period northeasterly swell will arrive late tonight into tomorrow, which, combined with the locally generated wind-waves, will promote the formation of life- threatening rip currents on Thursday.

Beach visitors are urged to swim only at beaches with lifeguards on duty, remain aware of surf conditions, and avoid venturing too far from shore.

SJU WATCHES/WARNINGS/ADVISORIES

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