textproduct: San Juan

KEY MESSAGES

Issued at 204 PM AST Sat Aug 22 2026

* Variable weather conditions are expected through this evening, with periods of passing showers and daytime heating effects.

* Hot and humid conditions will maintain an elevated heat threat across coastal and urban areas, with heat indices potentially reaching around 110F. A Heat Advisory is in effect for areas where the highest heat indices are expected from 10 AM to 5 PM AST today.

* A weak tropical wave will approach and move across the region on Monday, increasing moisture and the frequency of showers, although the deepest moisture is expected to remain mainly south over the Caribbean waters.

* A low risk of rip currents will continue across all beaches for the upcoming days.

Short Term(This evening through Monday)

Issued at 204 PM AST Sat Aug 22 2026

Generally calm weather conditions with only a few showers developed across Puerto Rico and the U.S. Virgin Islands during the morning hours. Despite the limited shower activity, the combination of available low- level moisture and high temperatures has allowed heat indices to climb into the 100 to 108 degree Fahrenheit range. Heat will therefore remain an important consideration for those spending extended periods outdoors through the remainder of the afternoon. Afternoon convection is starting to develop across western PR and the Culebra and Saint Thomas streamer also began to develop possibly affecting the metro area.

Tonight, precipitable water decreases and relatively dry air persists through the mid-levels. This will favor mostly dry and stable conditions overnight across Puerto Rico and the U.S. Virgin Islands.

On Sunday, warm conditions will continue as 925 mb temperatures rise into the two standard deviation criteria. Also, the weak 700 and 500 mb lapse rates around 5 degrees C/km and limited mid- level moisture should restrict instability and the coverage of showers and thunderstorms. Most areas should remain dry, although an isolated afternoon shower and thunderstorm cannot be ruled out. Regardless, heat will remain the more widespread concern during the daytime, and appropriate precautions should be taken during prolonged outdoor activities. Sunday night into Monday, models continue to suggest a slight increase in moisture across the islands as a weak tropical wave approaches the region. The flooding and lighting threat for that period remains limited.

Long Term(Tuesday through next Friday)

Issued at 204 PM AST Sat Aug 22 2026

The main long-term forecast concerns are persistent excessive heat and the evolution of the mid-level ridge as a couple of weak tropical disturbances move through the Caribbean. Confidence remains moderate through Tuesday, then decreases somewhat for the latter half of the week as model differences become more pronounced.

On Monday, the deterministic GFS suggests the mid-level ridge will erode by the afternoon. If this occurs, reduced mid-level inhibition combined with daytime heating and local effects should support a better opportunity for afternoon convection across the interior and western portions of Puerto Rico. Farther east, the U.S. Virgin Islands and windward portions of Puerto Rico should experience mainly isolated, fast-moving showers. Limited to elevated excessive heat conditions will remain a concern, particularly across coastal and urban areas.

By Tuesday, a weak tropical wave is forecast to approach the region. However, the deterministic GFS and ECMWF differ on the strength of the mid-level ridge and associated moisture. Nevertheless, increasing moisture should support showers and isolated thunderstorms across the U.S. Virgin Islands and eastern Puerto Rico as early as Tuesday morning, followed by additional convection over the interior and western portions of Puerto Rico during the afternoon. Confidence in rainfall coverage and amounts remains limited, however. The GFS is more aggressive in weakening the mid- level ridge, while guidance also suggests increasing trade winds. A faster low-level flow could limit rainfall duration and reduce the potential for significant accumulations.

Any rainfall would be beneficial given the ongoing drought conditions across portions of Puerto Rico and the U.S. Virgin Islands, particularly if precipitation occurs within reservoir watersheds. However, given the expected progressive nature of the showers and current model uncertainty, confidence remains low that this wave will provide meaningful drought relief.

Guidance generally favors the mid-level ridge rebuilding over the region Wednesday, which should once again suppress widespread convection while maintaining hot conditions. Another disturbance is being monitored for Thursday, although current GFS guidance keeps the bulk of its moisture and associated activity south of the local islands over the Caribbean Sea. Another possible tropical wave may approach Friday, but current guidance suggests limited organization and moisture. Given the lead time and model variability, confidence in the Thursday-Friday evolution remains low.

Overall, periods of excessive heat will remain one of the primary hazards during the long-term period, particularly Monday and Tuesday and potentially into Wednesday. Rainfall opportunities will increase at times with passing disturbances, but confidence in significant or widespread accumulations remains low.&&

AVIATION

(18Z TAFS) Issued at 204 PM AST Sat Aug 22 2026

Mainly VFR conds expected across all terminals thru the period. SHRA/TSRA development over W PR may result in brief MVFR conds at/near TJBQ aft 23/17Z. VCSH near TJSJ after 23/17Z. E winds 10-15 kt with higher gusts, becoming lighter overnight.

MARINE

Issued at 204 PM AST Sat Aug 22 2026

Showers and isolated thunderstorms moved across regional waters and local passages during the morning hours, though they have diminished. The latest scatterometer data shows mainly moderate winds across local Atlantic and Caribbean waters, while altimeter data reported seas between 3 and 5 feet. A surface high pressure over the Western Atlantic, combined with a low pressure across the central Atlantic, will continue to promote moderate E-ESE winds across the region for the rest of the weekend and early next week. As a surface high pressure strengthens, the local pressure gradient will likely increase, leading to moderate to locally fresh trades and choppy conditions; small craft must exercise caution. A weak tropical wave is expected to approach the local area by late Sunday into Monday, increasing frequency of showers across regional waters and passages.

BEACH FORECAST

Issued at 204 PM AST Sat Aug 22 2026

The beach forecast remains on track. The latest nearshore buoys reported seas between 2 and 3 feet during the morning hours, and based on local bathymetry, breaking waves should lead to a low rip current risk. Nevertheless, beachgoers should pay attention to beach conditions, as life-threatening rip currents can often occur near reefs, jetties, groins, and piers. The low risk is expected to continue for the rest of the weekend and early next week. As a surface high pressure builds in the western Atlantic and local pressure gradient increases, the risk will likely upgrade to moderate, particularly over northern and eastern-exposed beaches of Puerto Rico and the U.S. Virgin Islands. Residents and visitors are encouraged to opt for beaches with lifeguards, as life-threatening rip currents are possible along the surf zone. Besides rip currents, beachgoers should monitor the weather conditions, as showers and isolated thunderstorms are likely each afternoon, particularly near coastal areas of western Puerto Rico. Periods of heavy showers, gusty winds, and isolated lightning are likely, beachgoers must seek shelter whenever they hear thunder.

FIRE WEATHER

Issued at 204 PM AST Sat Aug 22 2026

Critical fuels continue across the islands, with moderate to extreme drought conditions. During the morning hours, moisture content gradually dropped, though they were brief and did not reach fire weather criteria. Additionally, winds picked up, between 10 and 15 mph, with gusts up to 20 and 23 mph. Due to abundant moisture lingering across the area, the risk for fire danger should remain low today; however, conditions may deteriorate tomorrow as a drier air mass filters into the region, becoming favorable for fire spread. Residents and visitors are urged to avoid outdoor burning, as conditions will enhance wildfire ignition and rapid spread.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007- 008-010>013.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...None.