textproduct: San Juan

KEY MESSAGES

Issued at 209 AM AST Wed Aug 19 2026

- A tropical wave (former Invest 94L) moving across the region, will bring periods of shower and isolated thunderstorms today.

- There is an elevated flooding risk across portions of central, western and northwestern Puerto Rico, particularly during the afternoon hours.

- A drier airmass will accompanied by low-to-moderate concentrations of Saharan dust will return tonight after the wave passage, persisting through the end of the week.

- There is a low risk of rip currents today across all beaches of Puerto Rico and the U.S. Virgin Islands.

Short Term(Today through Friday)

Issued at 209 AM AST Wed Aug 19 2026

A tropical wave (former Invest 94L), currently with its axis located over Puerto Rico, will continue to move westward across the region overnight and into the morning hours. An increase in shower activity is already visible on Doppler radar and satellite imagery, with isolated to scattered showers primarily affecting eastern and northern Puerto Rico, as well as the surrounding regional waters. No significant rainfall accumulations have been reported so far.

As the wave moves farther west, abundant tropical moisture will continue to filter into the region, increasing precipitable water (PWAT) values up to 2.25 inches. This wave is interacting with an upper-level trough to the northeast, increasing atmospheric instability aloft. This instability will be further supported by cooler mid-level temperatures (-7C at 500 mb), elevating the potential for thunderstorms across the area. Current weather patterns and the latest model guidance favor periods of moderate to heavy showers and isolated thunderstorms across eastern Puerto Rico and portions of the U.S. Virgin Islands during the morning. As the day progresses, this activity will shift toward central, western, and northwestern Puerto Rico during the afternoon. Additional shower and isolated thunderstorm development is expected across the San Juan metropolitan area due to streamer activity forming downwind of El Yunque. Consequently, there is an elevated flooding risk across western and northwestern Puerto Rico, alongside a limited risk across the eastern interior and southeastern portions of Puerto Rico and the U.S. Virgin Islands.

The moisture field from this tropical wave is expected to exit the area by this evening into Thursday, replaced by a drier airmass accompanied by low-to-moderate concentrations of Saharan dust. PWAT values will drop rapidly to well-below-normal levels around 1.25 inches, persisting through at least Friday. Meanwhile, a surface high-pressure system over the central Atlantic will maintain breezy east-southeastern winds through the end of the week.

Cloud cover and rainfall associated with the tropical wave may bring temporary relief from the recent warm spell. However, high temperatures and heat indices exceeding 100F remain possible across coastal and urban areas during the morning, depending on the extent of cloud cover. Once the wave passes, an elevated to significant heat risk is projected to return on Thursday and continue through the rest of the week. Residents and visitors are encouraged to monitor updating weather reports, take precautions against the heat, and stay hydrated.

Long Term(Saturday through Wednesday)

Issued at 209 AM AST Wed Aug 19 2026

A generally dry and breezy pattern is expected through the long-term period. Very dry mid-level conditions, warmer-than-normal temperatures aloft, and intermittent Saharan dust should limit the depth and coverage of convection, although patches of low-level moisture and a tropical wave crossing early next week may still support brief passing showers and localized afternoon development. No significant rainfall hazards are anticipated at this time.

Heat will remain the primary hazard, with elevated to locally significant heat risk possible where sufficient sunshine occurs. Persistent breezy winds, dry conditions, and limited wetting rainfall may also continue to support elevated fire weather concerns, particularly across the driest areas. Overall, hazards should remain focused on heat and fire weather rather than rainfall through the period.

AVIATION

(06Z TAFS) Issued at 209 AM AST Wed Aug 19 2026

Mainly VFR conds expected across all TAF sites through the forecast period. A tropical wave will move across the region today, resulting in periods of SHRA/TSRA. SHRA/VCSH expected to increase this morning at TJSJ/TIST/TISX aft 19/06Z. Aftn SHRA/TSRA, will result in VCTS at TJPS/TJBQ/TJSJ thru 19/22-23Z. This activity could result in brief MVFR/IFR conds. Light winds at 10 kt or less through 19/13Z. Winds E-ESE at 10-15 kt with sea breeze variations and ocnl gusts up to 25 kt through 19/23Z.

MARINE

Issued at 209 AM AST Wed Aug 19 2026

Light to moderate easterly trade winds will continue to prevail across the region over the next few days. Seas are expected to remain below small craft advisory criteria through the end of the week. Today, a weak tropical wave will continue to bring showers and thunderstorms across portions of the regional waters. This will elevate localized lightning hazards and bring gusty winds. From Thursday onward, expect hazy skies across the northeastern Caribbean due to moderate concentrations of Saharan dust.

BEACH FORECAST

Issued at 209 AM AST Wed Aug 19 2026

There is a low risk of rip currents today across all beaches of Puerto Rico and the U.S. Virgin Islands. However, the lightning potential will increase due to thunderstorm activity associated with the arrival of a tropical wave. Through the rest of the week, a low to moderate risk of rip currents is expected to prevail across all islands as winds and seas ease across most coastal waters. However, remember that even when the risk is low, life-threatening rip currents can occur near groins, jetties, reefs, and piers. Moderate concentrations of Saharan dust will promote hazy skies on Thursday and Friday.

SJU WATCHES/WARNINGS/ADVISORIES

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