textproduct: San Juan

KEY MESSAGES

Issued at 321 AM AST Tue Jun 30 2026

* Moderate to high concentrations of Saharan Dust will continue to filter across Puerto Rico and the U.S. Virgin Islands today, resulting in hazy skies, reduced visibility, and poor air quality. Sensitive groups must follow medical recommendations.

* Limited shower activity is expected across the islands today, however, localized afternoon showers and few isolated thunderstorms are possible across northwestern Puerto Rico.

* Warmer to hot conditions are expected for the next few days, with heat indices reaching or exceeding 105 degrees Fahrenheit across urban and low-lying areas of Puerto Rico and the U.S. Virgin Islands. Stay hydrated!

Short Term(Today through Thursday)

Issued at 321 AM AST Tue Jun 30 2026

Calm and quiet conditions prevailed overnight across Puerto Rico and the U.S. Virgin Islands under mostly clear to partly cloudy skies. A few isolated showers developed across the region but remained over the coastal waters. Overnight lows ranged from the upper 70s to low 80s in urban and coastal areas, and from the upper 60s to low 70s in the mountains. Winds were light and variable at 5 knots or less.

Today, moderate to high concentrations of Saharan dust will continue to filter into the islands, causing hazy skies, reduced visibility, and poor air quality. While these conditions will generally suppress rainfall, patches of moisture and a tropical wave moving south of the area will still trigger fast-moving, passing showers across the islands. Residents and visitors, particularly sensitive groups, including individuals with respiratory conditions, are urged to limit prolonged outdoor exposure and take necessary precautions.

A broad high-pressure system and a strengthening mid-level ridge will continue to maintain relatively drier conditions aloft, inhibiting the development of strong showers and limiting thunderstorms through Thursday. Under this pattern, passing showers will impact portions of eastern Puerto Rico and the U.S. Virgin Islands during the morning hours, followed by locally induced afternoon showers and thunderstorms across western and northwestern Puerto Rico.

Over the next few days, warm temperatures will persist, rising into the upper 80s and low 90s across coastal and urban areas, and into the low to mid-80s in the mountains. Heat indices are forecast to reach or exceed 105-111F, particularly during the peak heating hours of the day. Everyone is urged to practice heat safety by staying hydrated, limiting strenuous outdoor activities, and taking frequent breaks in shaded or air-conditioned areas.

Long Term(Friday through Tuesday)

Issued at 321 AM AST Tue Jun 30 2026

The long-term forecast remains on track. A transition from a relatively dry and hazy air mass to a highly saturated and unstable tropical environment is anticipated across the local area. At the surface, a dominant high pressure system over the Central Atlantic will maintain the local pattern under southeasterly winds, fluctuating at times, particularly during the morning hours. Aloft, a 250 mb cut-off low will remain anchored near the region throughout the entire forecast period, providing continuous upper-level support and maintaining a marginally unstable environment with 500 mb temperatures forecast to range between -8 C and -7 C. From Friday into Saturday, despite the instability aloft, available moisture will remain relatively shallow and trapped below the 850 mb level. The NASA Goddard aerosol model guidance again indicates a mass of Saharan dust moving across the region, which will promote hazy skies and effectively suppress widespread convective activity. Consequently, residents can expect a variable weather pattern characterized by hot conditions and limited rainfall accumulations, though brief morning showers across eastern Puerto Rico and isolated afternoon convection over the western interior and northwestern sectors cannot be entirely ruled out due to local effects and daytime heating.

From Sunday into Tuesday, the latest global model guidance from both the ECMWF and GFS indicates an increase in mid-level moisture, with increasing relative humidity values at the 700 mb level arriving in the region. This will enhance a variable weather pattern, boosting the development of afternoon convection across the western and northwestern interior of Puerto Rico. Meanwhile, Saharan dust concentrations will gradually diminish, allowing low-level moisture to become more uniform by Monday. By Tuesday, a significant increase in deeper atmospheric moisture is highly anticipated across the northeastern Caribbean as a tropical wave approaches and moves through the local area. The arrival of tropical moisture, combined with the favorable upper-level dynamics provided by the persistent cut-off low, will erode any remaining stable layers and allow precipitable water values to expand well above normal levels. This interaction will result in an increase in widespread shower and isolated thunderstorm activity across the region, bringing a limited to elevated potential for localized ponding of water on roadways and in poorly drained areas. Regardless of the changing moisture levels, persistently warm conditions will dominate coastal and urban sectors for the entirety of the long-term period. An elevated heat threat will remain present each day, with maximum heat index values consistently peaking between 100 and 108 F across portions of the north-central coastal plain and southern Puerto Rico during the peak heating hours.

AVIATION

(06Z TAFS) Issued at 321 AM AST Tue Jun 30 2026

VFR conds are expected to prevail across all TAF sites. Afternoon SHRA may result in VCSH at TJBQ & TJSJ btw 30/17-23Z. SE winds between 12-16 kt are expected with higher gusts and sea breeze variations. Winds will become light and variable at 5-10 kt aft 30/23Z.

MARINE

Issued at 321 AM AST Tue Jun 30 2026

The surface high pressure across the Central Atlantic as well as a frontal low over the western Atlantic will promote moderate to locally fresh east to east-southeasterly winds causing moderate chops or even choppy seas. Therefore, small craft should exercise caution. A dense Saharan Air Layer will deteriorate air quality on through tomorrow; additional concentrations are forecast to start to filter in on Friday and during the weekend.

BEACH FORECAST

Issued at 321 AM AST Tue Jun 30 2026

Throughout the rest of the workweek, most beaches across Puerto Rico and the U.S. Virgin Islands should remain with a low risk of rip currents. However, life-threatening rip currents often occur in the vicinity of groins, jetties, reefs, and piers. Only localized areas under a moderate risk of rip currents (rip currents are possible in the surf zone) are possible this workweek. The moderate risk should gradually spread to other beaches by the upcoming weekend, as the local pressure gradient increases and winds strengthen, with a moderate risk of rip currents across most beaches of the islands. Moderate to high concentrations of Saharan Dust will continue to gradually filter into the region, persisting through tomorrow, Wednesday; additional concentrations are forecast to start to filter in on Friday and during the weekend. These concentrations will result in hazy skies, reduced visibility, and poor air quality. High Heat Indices will continue during the next several days.

SJU WATCHES/WARNINGS/ADVISORIES

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