textproduct: San Juan

KEY MESSAGES

Updated at 327 AM AST Sun Jul 26 2026

* Dangerous heat will continue through Tuesday for the USVI and PR. Heat Advisories remain in effect today, and additional Heat Advisories or even Extreme Heat Warnings may be needed Monday and Tuesday, especially where rainfall is limited.

* A tropical wave will increase showers and thunderstorms from late Sunday through Tuesday. The greatest coverage is expected Monday and Tuesday, bringing an elevated risk of urban and small-stream flooding, with isolated flash flooding possible in areas of persistent heavy rainfall.

* Today's flooding threat will remain localized. Scattered afternoon showers and isolated thunderstorms may produce brief heavy rain, mainly across the San Juan metro area, east PR, and interior to northwestern Puerto Rico, leading to ponding of water and isolated urban flooding.

* Beachgoers should exercise caution due to a moderate risk of life-threatening rip currents across the north and south coast of PR and the St Croix.

Short Term(Today through Tuesday)

Issued at 327 AM AST Sun Jul 26 2026

The moderate concentrations of suspended Saharan dust led to warmer-than-normal nights, with lows in the low 80s and upper 70s in coastal and urban areas of the USVI and PR. A few showers developed around midnight and early in the morning near the northern and eastern coasts of PR, and some moved inland across the USVI. However, this activity was briefed. Skies were mostly clear, except for the clouds associated with the passing showers affecting the windward locations. Winds were mainly from the east to east-southeast across most local stations, at 5 to 15 mph, with land-breeze fluctuations.

Subsidence ahead of an approaching tropical wave will promote relatively quiet weather through much of Sunday morning, limiting convection to a few passing showers across the windward coasts. Additionally, warmer-than-normal overnight temperatures and the available moisture will contribute to dangerous heat between mid- morning and the afternoon. Consequently, a Heat Advisory remains in effect for portions of the forecast area.

By Sunday afternoon, the leading edge of deeper tropical moisture interacting with a lingering mid- to upper-level trough will support scattered showers and isolated thunderstorms. The greatest coverage is expected across the U.S. Virgin Islands surrounding waters, extending downwind of Vieques and the Luquillo Mountains into the San Juan metropolitan area, as well as across the interior and northwestern portions of Puerto Rico. Although locally heavy rainfall is possible, relatively dry mid-level air should limit convective coverage and duration, resulting in only a limited flooding threat. Localized ponding of water on roads and in poor-drainage areas will be the primary concern, without ruling out isolated urban flooding.

Conditions become increasingly favorable for more widespread convection beginning late Sunday night as deep tropical moisture overspreads the region. Moisture and instability will continue to increase through Monday and Tuesday as the tropical wave moves west-northwest across the northeastern Caribbean. This pattern will favor periods of scattered to numerous showers and isolated to scattered thunderstorms, particularly during the overnight and morning hours on Monday and again each afternoon through Tuesday. Therefore, an elevated risk of flooding is expected on both days, with urban and small-stream flooding becoming more likely, and a limited potential for isolated flash flooding where heavier, more persistent convection develops.

In addition to the rainfall threat, forecast 925-mb temperatures remain anomalously warm. Areas with limited rainfall will likely see above-normal daytime highs and unusually warm overnight lows. Combined with the increasing tropical moisture, these conditions will promote elevated to potentially significant heat impacts across portions of the islands. Additional Heat Advisories and possibly Extreme Heat Warnings may be required on Monday and Tuesday, depending on observed temperatures and heat index values.

Long Term(Wednesday through Sunday)

Issued at 327 AM AST Sun Jul 26 2026

Recent model guidance continues to suggest abundant moisture across Puerto Rico and the U.S. Virgin Islands as a tropical wave moves through the region early in the period. The latest precipitable water (PWAT) values are near 2.0 inches, reflecting normal to above- normal moisture for this time of year. Under this scenario, scattered trade wind showers remain possible during the morning, followed by afternoon showers and isolated thunderstorms across central and northwestern Puerto Rico driven by daytime heating and local effects.

However, these conditions will be short-lived as a drier air mass quickly moves into the area by Wednesday night. At the surface, a strengthening high-pressure system will tighten the pressure gradient, promoting breezy conditions through the rest of the period. Stability aloft will be further supported by a building mid- to-upper level ridge, limiting overall shower activity across the islands through the second half of the week as PWAT values drop below normal to 1.25-1.30 inches. Nonetheless, quick patches of moisture embedded in the trade winds will bring occasional fast- moving showers with minimal to no impact. Moisture levels should see a slight increase by late Saturday into Sunday as another tropical wave approaches the region. Near to above-normal temperatures will persist daily, with daytime highs reaching the upper 80s to low 90s across coastal and urban areas.

AVIATION

(06Z TAFS) Issued at 327 AM AST Sun Jul 26 2026

Mostly VFR conditions will prevail today. Expect E-ESE winds at 1020 kt with gusts up to 30 kts, btwn 26/13-23z. SHRA/TSRA are possible near IST/ISX/JSJ btwn 26/14-18z, spreading to the interior and NW-PR btwn 26/16-23z, bringing brief MVFR/IFR conditions and mountain obscurations. Activity will slowly increase aft 26/23z with the arrival of a tropical wave, creating an unstable and wet pattern.

MARINE

Issued at 327 AM AST Sun Jul 26 2026

Moderate to locally fresh easterly winds will continue to produce choppy seas and hazardous conditions for small craft across portions of the Atlantic waters, offshore Caribbean waters, and local passages through Sunday. An approaching tropical wave will increase showers and isolated thunderstorms late Sunday into Monday, creating locally higher winds and seas, frequent lightning, and reduced visibility in and near convection. Marine conditions are expected to improve briefly early next week as winds and seas subside before deteriorating again by midweek as easterly winds strengthen. Lingering low concentrations of Saharan dust may result in occasional hazy skies but are not expected to become a significant marine hazard.

BEACH FORECAST

Issued at 327 AM AST Sun Jul 26 2026

A moderate risk of rip currents continues across northern and eastern Puerto Rico, Vieques, Culebra, and St. Croix. As winds decrease early next week, the rip current risk should gradually lessen, resulting in improving beach conditions through midweek. However, life-threatening rip currents will remain possible near reefs, jetties, groins, and piers. The rip current risk is expected to increase again later in the workweek as easterly winds strengthen. Beachgoers should also remain alert for thunderstorms and heat.

FIRE WEATHER

Issued at 327 AM AST Sun Jul 26 2026

Despite relative humidity values remaining above critical thresholds, critically dry fuels continue to persist across southern Puerto Rico and St. Croix. Therefore, marginal fire weather conditions will continue, particularly where locally breezy winds develop during the afternoon.

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.