textproduct: San Juan

KEY MESSAGES

Issued at 335 AM AST Sun Aug 23 2026

* A heat threat is expected for today as well with warm temperatures with heat indices in the 105 to 111 degrees. Therefore, a heat advisory is in effect from 10 AM to 4 PM AST.

* Variable weather conditions are expected today as a weak tropical wave moves across the islands, bringing periods of increased shower activity.

* A wetter and more unstable pattern is expected from Tuesday into Wednesday, with an increased chance of showers and thunderstorms across the islands due to another tropical wave.

* A low to moderate risk of rip currents is expected over the coming days at local beaches.

Short Term(Today through Tuesday)

Issued at 335 AM AST Sun Aug 23 2026

During the overnight and early morning hours, some cloudiness was observed across eastern sections of Puerto Rico, although no significant rainfall activity was detected across the islands. In general, weather conditions remained fair, with only periods of passing cloudiness affecting portions of the region. Skies remained mostly clear to partly cloudy across the rest of Puerto Rico and the U.S. Virgin Islands. Overnight temperatures were in the lower 80s across coastal and urban areas. Meanwhile, temperatures dropped into the lower to mid-70s across the mountainous and interior sections of Puerto Rico. Winds were generally from the east at around 10 mph, with some variations associated with the land breeze along coastal areas.

For today, a surface high pressure over the western Atlantic, in combination with a low-pressure system over the central Atlantic, will continue to promote moderate easterly winds across the region. Under this surface pattern, the moisture field associated with a weak tropical wave is forecast to move across the islands, with precipitable water values increasing to around 1.7 to 1.9 inches. This increase in moisture will promote a more showery pattern, initially across the U.S. Virgin Islands during the morning hours before spreading across Puerto Rico and the rest of the local islands. Although surface conditions will remain favorable, a mid-level ridge will maintain some subsidence, potentially limiting the vertical development. Additionally, an /upper-level low over the Caribbean will promote diffluent flow, supporting periods of high-level cloudiness and providing some upper-level ventilation. Nevertheless, under the actual conditions, the forecast calls for local afternoon convection and isolated thunderstorms along western sections due to the local effects. In terms of heat threat, despite the expected increase in cloudiness and shower activity, a heat threat could still develop across several areas, particularly across north-central Puerto Rico and portions of the southern coastal plain. Conditions remain borderline between Limited and Elevated Heat Risk; therefore, a Heat Advisory is in effect from 11 AM through 4 PM AST.

By Monday, slightly drier conditions are expected as the moisture associated with the first tropical wave gradually moves away from the region. Nevertheless, enough low-level moisture will remain available to support passing showers, mainly across windward areas during the morning hours. This brief improvement will be short- lived, as another surge of tropical moisture associated with a second tropical wave is expected to reach the islands late Monday night into Tuesday. At the same time, winds will gradually shift from the east to the east-southeast, favoring increased moisture advection across the region. Current high-resolution guidance suggests an increase in shower activity across eastern Puerto Rico and the U.S. Virgin Islands by early Tuesday morning. As deeper moisture spreads across the area, a more active shower and thunderstorm pattern is expected throughout Tuesday, particularly where local and diurnal effects enhance convection.

Long Term(Wednesday through Sunday)

Issued at 335 AM AST Sun Aug 23 2026

During the long-term period, the weather pattern will be mainly dominated by high pressure across the central Atlantic and the passage of tropical waves, primarily from the east to southeast. Aloft, a mid-level ridge will dominate for most of the period.

By Wednesday, remnant moisture associated with a tropical wave will remain across the region. Current guidance indicates that precipitable water values will remain near seasonal levels; however, moderate to locally high concentrations of Saharan dust will persist across the region before decreasing Wednesday night into Thursday. As a result, mainly fair weather, hazy skies, and hot temperatures are expected across the U.S. Virgin Islands. Across Puerto Rico, expect passing morning showers over windward areas, with limited afternoon convection across western municipalities.

By Thursday, overall drier air will dominate, with PWAT values falling below seasonal averages. However, intermittent patches of moisture will continue to move across the region. An upper-level trough will linger, resulting in cooler 500-mb temperatures, while the mid-level ridge will still provide some stability. Despite this, diurnal heating and local effects will support the development of afternoon convection, including isolated thunderstorms across western Puerto Rico, which could result in a limited flood threat.

From Friday into Saturday, current model guidance suggests the arrival of a tropical wave, increasing tropical moisture up to 2.25 inches. Uncertainty remains in the forecast during this period, so residents and interests across the region are encouraged to continue monitoring the latest forecasts and the evolution of the tropical wave. By Sunday, precipitable water values are expected to decrease to seasonal or below-normal levels, limiting rainfall chances.

One persistent hazard throughout the period will be excessive heat, with an elevated heat threat expected on most days. Wednesday could pose a particularly significant heat threat due to above-normal 925- mb temperatures, southeasterly winds, the presence of Saharan dust, and seasonal moisture levels. Residents are encouraged to stay well hydrated, wear lightweight and loose-fitting clothing, take frequent breaks from the sun, and follow other heat-safety precautions.

AVIATION

(06Z TAFS) Issued at 335 AM AST Sun Aug 23 2026

VFR conds are expected to prevail across all taf SITES. Passing SHRA are expected across the USVI and E PR terminals during the morning hrs as moisture associated with a weak tropical wave moves across the region. Aft 23/16Z, diurnal heating and local effects will promote SHRA/TSRA development, mainly at/near TJBQ and TJSJ, with brief MVFR conds possible due to reduced VIS and lower CIGs. E winds at 10-15 kt will prevail, with Locally higher gusts are possible near the strongest SHRA/TSRA.

MARINE

Issued at 335 AM AST Sun Aug 23 2026

A weak tropical wave will approach the region later today and into tonight, bringing increased moisture and passing showers across the local waters. Moderate easterly trade winds will prevail through the rest of the weekend under the influence of surface high pressure over the Atlantic. However, winds may briefly weaken as the pressure gradient relaxes. Afterward, another tropical wave is forecast to approach the eastern Caribbean around Tuesday, bringing more moisture and shower activity along with gradually strengthening easterly winds.

BEACH FORECAST

Issued at 335 AM AST Sun Aug 23 2026

Beachgoers can expect a low risk of life-threatening rip currents through at least Tuesday as winds remain relatively light across the region. However, life-threatening rip currents may still occur, especially near groins, jetties, reefs, and piers. Always swim near a lifeguard and heed the advice of local beach patrol and flag warning systems.

The risk of life-threatening rip currents is expected to increase to moderate from Wednesday onward as easterly winds strengthen across Puerto Rico and the U.S. Virgin Islands.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon for PRZ001>003-005-007-008-010>013.

VI...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon for VIZ001-002.

AM...None.