textproduct: San Juan

KEY MESSAGES

Issued at 329 AM AST Sat Jun 27 2026

* A surface trough will move over the islands this morning, increasing moisture and shower activity. Winds will gradually veer during the morning as the trough axis moves westward, starting from the ENE and then becoming ESE by this afternoon.

* This flow will promote showers and isolated t-storms over interior to NW PR this afternoon, as well as lines of showers from El Yunque and the local islands, increasing the flooding risk.

* Warm weather conditions should prevail across the islands during the next several days, generating up to an elevated heat threat.

* Although drier conditions are expected on Sunday, an approaching tropical wave will once again increase moisture and flooding risk on Monday.

Short Term(Today through Monday)

Issued at 329 AM AST Sat Jun 27 2026

Shower frequency increased across most of the region overnight due to an approaching surface trough. This system is expected to cross the islands this morning, sustaining elevated moisture levels and shower activity. Precipitable water (PWAT) values are forecast to remain within normal ranges (up to approximately 1.9 inches), potentially reaching slightly above-normal levels during this afternoon's convection. As the trough axis shifts westward, morning winds will gradually veer from the ENE to the ESE by this afternoon. While 925 mb wind speeds may decrease slightly, they will remain within seasonal norms. This ESE steering flow will direct showers toward windward sectors, as well as triggering convective showers and isolated t-storms over interior and W-NW Puerto Rico later today. Additionally, lines of showers can form off El Yunque and the local islands. These conditions will elevate the risk of flooding, resulting in possible urban and small stream flooding, as well as water ponding on roadways and in areas with poor drainage.

A drier air mass is expected to reach the area late tonight and Sunday, resulting in a more typical dry weather pattern with low concentrations of Saharan Dust. Residents can anticipate morning showers in windward sectors, followed by isolated afternoon convective showers across interior and W-NW Puerto Rico. ESE breezes will also reintroduce a low concentration of Saharan dust to the area. Current guidance indicates that a tropical wave, its associated moisture field and an approaching upper trough will affect the region on Monday, leading to a notable rise in deep- layer moisture over the local islands. Consequently, precipitable water (PWAT) levels are expected to climb to above normal values while 500 mb temperatures cool to more normal values, providing further support for convective activity during the afternoon hours. Furthermore, relative humidity and lapse rates in the 700-500 mb layer is projected to exceed seasonal norms. This surge in moisture will again increase the flooding risk and can result in more widespread showers and t-storms as well as afternoon convection over interior to western and northwestern Puerto Rico as well as downwind of the local islands and El Yunque. Localized water ponding as well as flooding can occur on roads and in areas with poor drainage. An elevated heat risk will persist during the period as 925 mb temperatures are forecast at above normal values each late morning to afternoon. This level of heat affects most individuals sensitive to heat, especially those without effective cooling and/or adequate hydration.

Long Term(Tuesday through Saturday)

Issued at 329 AM AST Sat Jun 27 2026

During the long-term period, a surface high pressure system centered over the central Atlantic and extending into the Caribbean will maintain a southeasterly low-level wind flow (03 km) across Puerto Rico and the U.S. Virgin Islands. Aloft, nearly zonal flow at 200 mb is expected on Tuesday and Wednesday, providing little in the way of upper-level support for organized convection. Lingering moisture associated with the previous tropical wave will remain over the region on Tuesday, with precipitable water values around 1.8 inches supporting scattered showers, primarily during the afternoon across western and interior Puerto Rico. Although moisture will gradually decrease by Thursday, sufficient low-level moisture will remain to support isolated to scattered afternoon convection, but widespread rainfall activity is not anticipated. Meanwhile, a moderate concentration of Saharan dust is expected to spread across the islands Tuesday and Wednesday, resulting in hazy skies and limiting overall convective development.

Despite the presence of Saharan dust, the persistent southeasterly flow will continue to promote a warm pattern, with above-normal temperatures and elevated heat indices across urban and coastal sections. Consequently, an elevated heat threat is expected to persist through the middle of the week. By Friday into Saturday, a drier air mass will move into the region, reducing precipitable water values and limiting shower activity across the local islands. In addition, the NASA Goddard Earth Observing System (GEOS) Model V5 continues to suggest another pulse of Saharan dust arriving late Friday into Saturday, reinforcing the drier pattern while maintaining hazy skies.

AVIATION

(06Z TAFS) Issued at 329 AM AST Sat Jun 27 2026

Mainly VFR conditions. Passing -SHRA/VCSH across windward terminals today as a surface trough moves over the islands. After 27/16Z, -TSRA/VCTS over TJBQ and possibly over TJSJ, prompting possible brief MVFR conditions. Winds will gradually veer this morning as the trough axis moves westward, starting from the E to ENE, and then becoming ESE at around 12 to 17 kts with higher gusts and sea breeze variations; winds decreasing after 27/23Z to 5 to 12 kts, with land breezes.

MARINE

Issued at 329 AM AST Sat Jun 27 2026

A surface trough moving near the northeastern Caribbean will weaken the local pressure gradient associated with the Atlantic high pressure system. As a result, moderate east to east-northeast winds are expected from today. The trough will also enhance shower activity across the regional waters, with the potential for isolated thunderstorms. By Sunday, moderate east to east-southeast winds will return as the Atlantic high pressure system reestablishes itself. Another tropical wave is expected to move across the region on Monday, bringing another increase in showers and the potential for isolated thunderstorms.

BEACH FORECAST

Issued at 329 AM AST Sat Jun 27 2026

A low risk of rip currents is expected along most local beaches through the weekend. However, even when the risk is low, isolated life-threatening rip currents can still occur, especially near jetties, groins, reefs, and piers.

A moderate rip current risk is forecast to develop for some beaches early next week, meaning life-threatening rip currents will become possible. Beachgoers are encouraged to swim near a lifeguard, heed posted warning flags, and follow the guidance of local beach patrols.

Hot and humid conditions may produce dangerous heat levels at the beaches. Stay hydrated, seek shade frequently, wear lightweight clothing, and limit prolonged sun exposure during the hottest part of the day.

In addition, isolated thunderstorms may develop this afternoon, mainly across northern and western Puerto Rico. If you are at the beach or participating in outdoor activities, remain alert for lightning. Remember: If you can hear thunder, you are close enough to be struck by lightning. Move to a substantial building or a hard- top vehicle immediately and remain there until 30 minutes after the last rumble of thunder.

FIRE WEATHER

Issued at 329 AM AST Sat Jun 27 2026

A surface trough will move over the islands today, bringing a moisture field that will be over the region through early tonight and providing some relief in terms of RH values. As the trough axis crosses the islands, winds will veer from ENE to ESE later today. Once winds veer to become more ESE, they will increase to 10 to 20 mph, with higher gusts. This wind direction could steer some passing showers over the region and provide some relief to the SW coastal plains today, the SE coastal plains have been receiving passing showers during the overnight hours. Although low, rainfall accumulations where detected by radar yesterday afternoon over the SW coastal plains. Nevertheless, relative humidities in the 40s to low 50s continue to be possible at times. Drier conditions expected tomorrow, Sunday, prompting a possible high fire danger risk. Up to a moderate fire danger risk is forecast today, please continue to monitor for any updates.

SJU WATCHES/WARNINGS/ADVISORIES

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