textproduct: San Juan

KEY MESSAGES

Issued at 250 AM AST Sun Jun 21 2026

* Father's Day is expected to bring the most active weather of the forecast period as a tropical wave moves across the region. Periods of heavy to torrential rainfall, thunderstorms, urban and small-stream flooding, and isolated flash flooding are possible across portions of Puerto Rico and the U.S. Virgin Islands.

* Moderate concentrations of Saharan dust will continue to affect the region early this week and possibly the second part of the week, resulting in hazy skies, reduced visibility, and degraded air quality, particularly for sensitive groups.

* Dangerous heat index values will continue each afternoon, especially between 10 AM and 4 PM, as hot temperatures combine with tropical moisture. Heat-related illnesses are possible without adequate hydration, cooling, and frequent breaks from the heat.

* Another tropical wave may approach the region by the middle of the week, bringing an additional chance for showers and thunderstorms. Forecast details will continue to be refined as confidence increases.

* Life-threatening rip currents will remain possible at exposed beaches through much of the week due to persistent moderate to locally breezy winds. Beachgoers should swim near lifeguards, heed warning flags, and follow local beach safety guidance.

Short Term(Today through Tuesday)

Issued at 250 AM AST Sun Jun 21 2026

Overnight, we had little or no rain and warm overnight temperatures as a drier air mass with moderate concentrations of suspended Saharan dust particles lingered across PR and the USVI. The Doppler Radar detected showers approaching the St Croix surrounding waters, with some moving inland as the tropical wave filters across the region. Once again, as we write the discussion, overnight temperatures ranged from the mid- to upper 70s to the low 80s along the coast, and from the mid- to upper 60s to the low 70s along the mountains. Most wind stations reported east to east-southeast winds of 5 to 15 mph, with fluctuations due to land breezes. Meanwhile, some stations in Culebra, St. Thomas, and St. John reported east to east-northeast winds around 15, with higher gusts.

The best chance for widespread and beneficial rainfall will occur today, Father's Day, as a tropical wave moves across Puerto Rico and the U.S. Virgin Islands. Although the wave is embedded within moderate to high concentrations of Saharan dust, an accompanying surge of moisture with precipitable water values between 1.85 and 2.05 inches will support passing showers across the U.S. Virgin Islands and eastern Puerto Rico, followed by afternoon convection over western Puerto Rico and downwind of El Yunque. While rainfall will be beneficial for areas experiencing abnormally dry or moderate drought conditions, urban and small- stream flooding, as well as isolated flash flooding, remain possible where persistent downpours and thunderstorms develop.

By Monday, the tropical wave will move away into the central Caribbean, while moderate concentrations of Saharan dust continue to affect the region. Hazy skies, reduced visibility, and poor air quality are expected, particularly for sensitive groups and those with respiratory conditions. Breezy east to east-southeast winds will persist as a strong Atlantic high pressure system maintains a tight local pressure gradient.

On Tuesday, a relatively stable and drier air mass will prevail across the islands as mid-level ridging strengthens and an upper-level low lifts farther north of the region. Passing trade- wind showers will continue to affect windward and eastern areas, while leeward sections experience mostly fair weather. Seasonably warm temperatures will persist, with highs reaching the upper 80s to low 90s across coastal and urban locations.

Long Term(Wednesday through Sunday)

Issued at 250 AM AST Sun Jun 21 2026

A tropical wave is forecast to move across the region on Wednesday and Thursday. While the wave will bring an increase in low-level moisture and result in a higher frequency of passing showers, model guidance suggests precipitable water values will remain near seasonal levels. In addition, mid-level relative humidity is expected to remain relatively low, while temperatures near 500 mb stay close to normal, limiting the potential for widespread deep convection. As a result, periods of passing showers are expected, particularly across windward and eastern sections during the morning hours and across western Puerto Rico during the afternoon due to local effects. However, significant rainfall accumulations are not anticipated at this time.

Dust aerosol model guidance suggests that low to moderate concentrations of Saharan dust may reach the local islands by Thursday. The arrival of this dust could promote hazy skies and occasionally reduced visibility while also contributing to a more stable atmosphere. Although the tropical wave is expected to enhance shower activity, the extent to which rainfall associated with the wave offsets the effects of the dust remains somewhat uncertain. Therefore, residents and visitors are encouraged to continue monitoring the latest forecasts for updates regarding both rainfall potential and air quality conditions. At this time, the highest concentrations of Saharan dust will Friday. Therfore, those with respiratory conditions are urged to follow the health experts recommendations and avoid outdoor activities.

By Friday and continuing through Saturday, moisture levels are expected to remain near to slightly below seasonal normals while relatively dry mid-level air persists across the region. This should support a decrease in shower coverage and a return to a more typical trade-wind weather pattern. Nevertheless, patches of shallow moisture embedded within the trades may still result in brief passing showers across windward areas from time to time. Temperatures will continue near seasonal normals. While no significant weather impacts are anticipated through the end of the forecast period, those planning outdoor activities should remain aware of passing showers and any lingering hazy conditions that could produce localized visibility reductions.

AVIATION

(06Z TAFS) Issued at 250 AM AST Sun Jun 21 2026

A tropical wave will bring SHRA/-SHRA, first across ISX, and later this morning near IST, spreading into eastern PR< where JSJ will possibly be affected by this activity. There is a good chance of observing TSRA/+TSRA from mid-morning into the afternoon across the interior sections of PR, but the USVI could see it, mainly across the surrounding waters. Winds will be from the E-ESE at 5 to 15 kt through 21/13z, then at 10-20kt with gusts up to 30 kt, especially around SHRA/TSRA and due to sea breeze.

MARINE

Issued at 250 AM AST Sun Jun 21 2026

A broad surface high pressure system building across the central Atlantic will continue to promote moderate to locally fresh easterly to east-southeasterly winds over the next several days. These conditions will maintain choppy seas across the local waters and Caribbean passages, and small craft should exercise caution. Meanwhile, moderate to occasionally high concentrations of Saharan dust will persist through the weekend and into early next week, resulting in hazy skies, reduced visibilities, and degraded air quality. A tropical wave moving across the Caribbean Sea today into Monday will increase moisture across the region, leading to a higher likelihood of showers and isolated thunderstorms over the regional waters.

BEACH FORECAST

Issued at 250 AM AST Sun Jun 21 2026

A moderate risk of rip currents continues for the north and east- facing beaches of Puerto Rico, including Vieques and Culebra, and across the U.S. Virgin Islands, while a low risk remains along the south and west coasts of Puerto Rico. Life-threatening rip currents remain possible along beaches with a moderate risk. On Sunday, increasing showers are expected across eastern Puerto Rico, while isolated thunderstorms may develop over northwestern Puerto Rico during the afternoon hours. In addition, moderate to high concentrations of Saharan dust will continue to move across the region, resulting in hazy skies, reduced visibility, and poor air quality.

FIRE WEATHER

Issued at 250 AM AST Sun Jun 21 2026

A tropical wave will bring beneficial rains across portions of the islands today. Winds will prevail mainly from the east to east- southeast at 10 to 20 mph, with gusts up to 33 mph, especially from mid morning into the afternoon. The tropical wave will maintain RH values above critical levels.

SJU WATCHES/WARNINGS/ADVISORIES

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