textproduct: San Juan

KEY MESSAGES

Issued at 235 AM AST Mon Jul 6 2026

* Dangerous heat will be the primary weather hazard today. A Heat Advisory is in effect today as hot temperatures combine with increasing humidity to produce dangerous heat indices. Similar conditions are expected Tuesday, with warm to hot conditions likely continuing through the remainder of the week.

* Moderate to locally high concentrations of Saharan dust will produce hazy skies, reduced visibility, and degraded air quality through Tuesday. A brief improvement is expected Wednesday before dusty conditions return late Wednesday into Thursday.

* A fast-moving tropical wave may bring a brief increase in showers and thunderstorms on Wednesday, with isolated lightning, locally heavy rainfall, and localized urban and small-stream flooding possible.

* Breezy easterly winds will continue each day, creating choppy marine conditions and maintaining a moderate risk of rip currents at most local beaches.

Short Term(Today through Wednesday)

Issued at 235 AM AST Mon Jul 6 2026

Overnight, breezy easterly trade winds steered a few fast-moving showers across the local waters and windward areas with little to no impacts. More importantly, persistent high-level cloudiness, warm surrounding waters, and continued onshore flow limited nocturnal cooling, with many coastal locations only falling to around 80 to 82 degrees. The lack of overnight relief, combined with a shallow increase in low-level moisture confined below 850 mb, will result in higher humidity and dangerous heat indices today despite having little impact on rainfall potential. Afternoon temperatures will once again climb into the upper 80s and lower 90s, while moderate to high concentrations of Saharan dust and persistent dry mid-level air continue to promote hazy skies, degraded air quality, and suppress widespread shower and thunderstorm development. A Heat Advisory remains in effect for portions of the islands today as dangerous heat becomes the primary weather hazard. Similar conditions are anticipated again on Tuesday. Breezy easterly trade winds will persist each day, with the strongest gusts developing during the early afternoon due to local sea-breeze influences.

A brief transition is expected on Wednesday as a fast-moving tropical wave crosses the eastern Caribbean, bringing a temporary increase in moisture and instability. This may result in increased showers and isolated thunderstorms, with localized urban and small-stream flooding and frequent lightning becoming the primary weather hazards. Heat will remain a concern, especially across coastal and urban areas, before another surge of drier air and Saharan dust spreads across the region Wednesday night, quickly restoring hazy skies, degraded air quality, and a hotter, more stable weather pattern.

Long Term(Thursday through Monday)

Issued at 235 AM AST Mon Jul 6 2026

The long-term forecast remains on track, with no significant changes introduced since the previous discussion. A building surface high pressure system north of the region will maintain a tight pressure gradient, promoting breezy to windy conditions across the islands through the first half of the long-term period. Winds are expected to prevail from the east-east southeast through Saturday, before veering from the east-northeast from Sunday into Monday morning.

On Thursday, moisture associated with the northern periphery of a passing tropical wave will approach the region. Nonetheless, the bulk of the moisture from this wave is expected to remain well south of the area over the Caribbean Sea, keeping local impacts minimal. The latest precipitable water analysis indicates below-normal moisture for the period, with precipitable water (PWAT) values dropping to 1.25 to 1.30 inches on Thursday. Therefore, no significant flooding impacts are expected with this wave.

Following the passage of the wave, a mid-level ridge is expected to strengthen, promoting drier and more stable conditions through the remainder of the period. From Friday onward, a drier air mass will begin to filter into the region alongside a dense plume of the Saharan Air Layer (SAL). Moderate to high concentrations of dust will reach the area throughout the weekend, promoting hazy skies, reduced visibilities, and poor air quality. Sensitive groups, particularly those with respiratory issues or allergies, should take necessary precautions to limit outdoor exposure.

Conditions will remain very similar throughout the weekend, with a slight increase in moisture expected by the beginning of next week as another disturbance approaches the islands. Temperatures at 925 mb will remain within seasonal values during the period, with maximum temperatures reaching the upper 80s and low 90s across coastal and urban areas, and the low to mid-80s in the mountains. However, heat indices are forecast to reach or exceed 100F each afternoon. Residents and visitors are strongly urged to practice heat safety by staying hydrated, limiting strenuous outdoor activities, and taking frequent breaks in shaded or air-conditioned areas.

AVIATION

(06Z TAFS) Issued at 235 AM AST Mon Jul 6 2026

VFR conditions will prevail at all TAF sites through the forecast period. Moderate to high concentrations of SA dust will continue to produce HZ and reduce VIS at times. Brief VCSH are possible in the vicinity of TJSJ and TJBQ between 16-22Z. E-ESE winds of 10-18 kt will become locally gusty after 14Z due to sea-breeze development, with the strongest gusts during the afternoon.

MARINE

Issued at 235 AM AST Mon Jul 6 2026

A broad surface high pressure building over the central Atlantic will promote a moderate to locally fresh east to east-southeast winds, resulting in choppy seas for the next several days. By the middle of the week, an approaching tropical wave will increase the shower and thunderstorm activity across regional waters that may lead to locally hazardous marine conditions. Meanwhile, moderate to high concentrations of Saharan Dust will linger across the region through mid week, bringing hazy skies, reduced visibility and poor air quality.

BEACH FORECAST

Issued at 235 AM AST Mon Jul 6 2026

The beach forecast continues on track. As winds continue to strengthen, the moderate risk of rip currents will continue across most beaches of Puerto Rico and the U.S. Virgin Islands. As mentioned in previous discussions, beachgoers must exercised caution, as life-threatening rip currents remain possible along the surf zone. Based on the latest model guidance, winds will likely remain strong, leading to breaking waves between 3 and 5 feet, for the next few days. Besides rip currents, beachgoers should remain weather alert, particularly for elevated heat risks today and the arrival of a tropical wave that will increase shower and thunderstorm activity and may move near coastal areas of the islands on Wednesday. Additionally, moderate to high concentrations of SAL will linger throughout the week, with the lowest concentrations on Wednesday. Sensitive groups must continue to follow medical recommendations.

FIRE WEATHER

Issued at 235 AM AST Mon Jul 6 2026

Weather conditions will be less supportive of rapid wildfire growth today and Tuesday as low-level moisture and relative humidity increase. However, critically dry fuels and severe soil moisture deficits persist across portions of southern Puerto Rico, with Keetch-Byram Drought Index (KBDI) values remaining above 550 and locally exceeding 660. Any fire that develops may still spread through the dry vegetation, particularly across the southern coastal plains and adjacent lower elevations, although increased humidity should limit fire growth compared to recent days. Residents and visitors should continue to avoid outdoor burning and exercise caution with any activity capable of producing sparks or open flames.

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.