textproduct: San Juan

KEY MESSAGES

Issued at 150 PM AST Mon Aug 10 2026

- Warm to hot conditions will continue this workweek across the islands, particularly over urban and low-lying areas. The Heat Advisory remains in effect through 4:00 PM AST.

- Frequency of showers and isolated thunderstorms will likely increase early Tuesday, increasing flood and lightning potential.

- Marine and coastal conditions may deteriorate by the end of the workweek into the weekend as stronger trade winds build seas and increase the rip current risk.

- The NOAA NHC continues to monitor multiple Atlantic disturbances; it remains too early to determine any impacts to Puerto Rico or the U.S. Virgin Islands.

Short Term(This evening through Wednesday)

Issued at 150 PM AST Mon Aug 10 2026

An elevated heat threat alongside fluctuating moisture and Saharan dust concentrations will dominate the short-term forecast period. Upper-air atmospheric soundings and satellite observations indicate precipitable water values fluctuating between 1.50 and 1.80 inches, capped somewhat by weak mid-level lapse rates around 5.0 to 5.5C/km and a persistent low-level trade wind inversion. Strong solar heating pushed temperatures into the upper 80s to mid-90s across the lower elevations today. This, combined with enough surface moisture, increased heat indices between 106112F along coastal and urban zones. A Heat Advisory remains in effect across low-lying terrain of all islands. The heat threat will persist for the next few days, and warmer 925mb temps are expected on Wednesday, and an Excessive Heat Warning could be required.

In terms of precipitation, it will vary noticeably over the next 72 hours. Drier air and Saharan dust following a departing tropical wave will limit convective coverage today to isolated diurnal afternoon showers over western Puerto Rico. However, latest global model guidance and high-resolution ensemble show a tropical wave with a surge in moisture crossing the local region on Tuesday, raising precipitable water levels near 2.00 inches. Strong daytime heating, sea breeze convergence, and terrain-forced uplift interacting with this tropical moisture will trigger and increase the coverage of showers and thunderstorms on Tuesday afternoon. The strongest cells will be capable of producing frequent cloud-to-ground lightning, gusty winds, and localized 1 to 2-inch rainfall accumulations, creating a heightened potential for ponding of water on roads and minor urban or small-stream flooding across the interior and western Puerto Rico.

By Wednesday, aerosol guidance and normalized moisture anomaly fields indicate a slot of drier, dust-laden Saharan air overspreading the region behind the departing wave. Precipitable water values will drop back below seasonal averages, capping widespread deep convection and restricting shower activity to brief passing early morning trade showers across windward areas and isolated afternoon convection along the western mountains. Pulses of suspended Saharan dust will maintain hazy skies and keep surface visibilities periodically reduced near 6 statute miles through the end of the short-term period.

Long Term(Thursday through next Sunday)

Issued at 210 AM AST Mon Aug 10 2026

A tightening pressure gradient associated with the Atlantic ridge will support breezy easterly to southeasterly winds Thursday into the weekend. A drier air mass and Saharan dust will dominate, with precipitable water values dropping to around 1.3 inches Thursday and only brief patches of low-level moisture thereafter. Shower activity should remain limited, with mainly passing showers and very localized afternoon convection. Fewer clouds, warm low-level temperatures, and sufficient low-level humidity will maintain an elevated to significant heat risk, especially across coastal and urban areas, where heat indices could approach 114 degrees. Strengthening trades will also lead to deteriorating marine and coastal conditions late in the week, with building seas and an increasing rip current risk.

Forecast confidence decreases late in the period as NHC continues to monitor multiple disturbances across the central and eastern tropical Atlantic. Guidance suggests that one of these systems could approach the northeastern Caribbean early next week, but considerable uncertainty remains regarding its track, strength, timing, and any potential local impacts. Therefore, the forecast for Monday and beyond may change depending on how these systems evolve.

AVIATION

(18Z TAFS) Issued at 150 PM AST Mon Aug 10 2026

Mainly VFR conditions are expected to prevail across all terminals during the next 24 hours. Mostly VCSH expected across all terminals through 10/22z due to shallow/locally induced -SHRA. The 10/12z TJSJ sounding indicated east winds up to 30 kt blo FL100. HZ due to Saharan dust will continue through the period, and VSBY may drop to 6SM.

MARINE

Issued at 150 PM AST Mon Aug 10 2026

The broad Atlantic ridge extending from the western into the central Atlantic will continue to promote moderate to locally fresh easterly winds tonight, becoming moderate on Tuesday as the local pressure gradient slightly weakens. A tropical wave crossing the eastern Caribbean Tuesday into Wednesday will increase the potential for showers and thunderstorms over the local waters. Followed by the tropical wave, winds will begin increasing again Wednesday night as the pressure gradient tightens, becoming fresh to locally strong by Thursday night into Friday. Choppy to rough seas across the regional waters and local passages are likely, leading to hazardous conditions for small craft.

BEACH FORECAST

Issued at 150 PM AST Mon Aug 10 2026

The beach forecast remains on track. The latest nearshore buys reported seas between 2 and 3 feet, leading to breaking waves up to 4 feet. Hence, the moderate risk of rip currents continues across northern and eastern beaches of Puerto Rico, including Vieques and Culebra, and the U.S. Virgin Islands. When visiting a beach under a moderate risk, beachgoers should pay attention to the beach conditions as life-threatening rip currents remain possible along the surf zone. Although winds may weaken on Tuesday, the moderate risk should continue for the next few days. Model guidance suggests strengthening winds, which could potentially increase breaking waves and lead to a high risk of rip currents this weekend. Residents and visitors should stay up to date with the latest issuance of the beach forecast.

Besides rip currents, beachgoers should stay weather alert, particularly on Tuesday and Wed, as the approach of a tropical wave will likely increase the likelihood of showers and isolated thunderstorms moving near coastal areas of the islands. Periods of heavy rainfall, gusty winds, and lightning could become hazardous, beachgoers should seek shelter whenever they hear thunder.

FIRE WEATHER

Issued at 150 PM AST Mon Aug 10 2026

The islands continue with critical fuels as moderate to extreme drought levels persist. The latest satellite-derived products show lingering moisture associated with a tropical wave across the CWA, with a drier airmass in the low to mid levels filtering into the region. Nevertheless, RH values dropped during the morning hours, particularly across the southern coastal plains of Puerto Rico, below thresholds (< 55%). Additionally, breezy to locally windy conditions continue across the islands, as RAWs stations reported winds between 15 - 25 mph and gusts up to 35 mph. Taking into consideration the dry fuels and KDBIs well above thresholds, the fire danger threat should remain elevated today; the Fire Danger Statement continues in effect through 5 PM AST. Residents and visitors are encouraged to avoid outdoor burning, as conditions will likely be favorable for wildfire ignition and rapid spread.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory until 4 PM AST this afternoon for PRZ001>005-007- 008-010>013.

VI...Heat Advisory until 4 PM AST this afternoon for VIZ001-002.

AM...None.