textproduct: San Juan

KEY MESSAGES

Issued at 110 AM AST Tue Jun 9 2026

* Dangerous heat will continue through at least midweek. Heat indices will exceed 100F, especially across urban, coastal, and lower- elevation areas of Puerto Rico and the U.S. Virgin Islands. Therefore, a Heat Advisory is in effect through 5 pm today.

* An increase in moisture and instability is expected late Wednesday and Thursday, increasing the potential for showers and thunderstorms. The greatest impacts are expected across interior and western Puerto Rico during the afternoon and evening hours.

* Traces of Saharan dust will persist through the forecast period, producing somewhat hazy skies and reduced air quality, especially through tomorrow.

* Another increase in moisture is possible Sunday into Monday, supporting a return to a more active pattern of passing showers and afternoon thunderstorms across portions of Puerto Rico and the U.S. Virgin Islands.

Short Term(Today through Thursday)

Issued at 110 AM AST Tue Jun 9 2026

Overnight, tranquil weather conditions prevailed across Puerto Rico and the U.S. Virgin Islands under mostly clear skies and light, variable winds. Temperatures remained in the upper 70s to low 80s across coastal and urban areas, while mountainous locations cooled into the 60s and low 70s.

Today through early Wednesday, the main concern will continue to be the heat. Above-normal temperatures, limited rainfall activity, and lingering Saharan dust will support hazardous heat conditions across coastal, urban, and lower elevation areas. Model guidance shows below-normal moisture levels, with precipitable water and 500 mb relative humidity values near or below the 25th percentile for this time of year, while 925 mb temperatures remain above normals. Consequently, dangerous heat indices are expected each afternoon, prompting the issuance of a Heat Advisory to highlight the elevated risk of heat-related illnesses, particularly for vulnerable populations and those without adequate cooling or hydration. Residents and visitors are urged to stay hydrated, avoid prolonged outdoor exposure during peak heating hours, and monitor sensitive individuals. Although overall conditions will remain mostly dry, a few quick-moving showers may affect windward areas during the morning, followed by isolated afternoon convection across western Puerto Rico.

By late Wednesday into Thursday, conditions may become slightly more unstable as a polar trough over the western Atlantic amplifies and approaches the northeast Caribbean. This feature is expected to enhance mid- and upper-level support across the region, increasing the potential for afternoon showers and thunderstorms, mainly across interior and western Puerto Rico. While precipitable water values are forecast to remain near seasonal levels, the added instability could still lead to more active afternoon convection. At this time, the risk for significant widespread flooding remains low. However, stronger showers and thunderstorms may produce localized ponding of water on roads as well as flooding in urban areas, small streams, and washes. Residents and visitors should continue monitoring the latest forecasts for updates as conditions evolve.

Long Term(Friday through Tuesday)

Issued at 110 AM AST Tue Jun 9 2026

No major changes were made to the long-term forecast, as weather conditions are expected to become drier and more stable over the upcoming weekend and early next week. A surface high pressure building over the Western Atlantic should increase the local pressure gradient, leading to strengthening east-southeast winds and resulting in breezy to locally windy conditions across the islands. Friday has the highest potential for flooding and lightning, as lingering moisture associated with a tropical wave and the proximity of an upper-level trough should enhance afternoon convection. From the latest model guidance, PWAT may vary between 1.7 and 1.9 inches, which is typical for this time of the year, but shows abundant low to mid-level moisture. Due to the proximity of the trough, mid-level temperature should remain cooler than normal (500 mb temperatures around -8 degrees Celsius), with enhanced vorticity, rising air, and divergence aloft across the region, favorable for deep convection. Additionally, the Galvez-Davison Index (GDI) suggests the potential of isolated to scattered thunderstorms, particularly over the western/northwestern side of the CWA in the afternoon. Although a drier airmass will gradually filter into the region on Friday, passing showers can still be expected during the morning hours over windward sections of the islands, followed by afternoon convection over interior and western/northwestern Puerto Rico. Additionally, island streamers may develop and bring some showers into eastern portions of Puerto Rico, including the San Juan Metropolitan area. Rainfall accumulations could lead to ponding of water over roadways and poorly drained areas, including minor flooding, over the aforementioned areas. As the drier air mass continues to filter into the region, patches of moisture may arrive throughout Saturday, with shallow afternoon convection over western/northwestern Puerto Rico. Sunday and Mondays forecast remains uncertain, as the latest global model solutions show different outcomes for the CWA. The latest GFS solution showed the upper-level trough lingering near the region, with PWAT values remaining near above normal (up to 1.9 inches), while the ECMWF solution suggests a mid-level ridge near the CWA, with drier air in the 850 - 500 mb layer. Due to inconsistency with the GFS solutions, Sunday and Mondays forecast was based on a similar pattern to Saturday, with limited rainfall activity.

In terms of heat, warmer conditions may persist throughout the forecast period as model guidance suggest typical to above normal 925 mb temperatures. With the available moisture, heat indices above 100 degrees Celsius cannot be ruled out, particularly across urban and lower elevations of the islands. Hence, residents and visitors should exercise caution as these levels could impact most individuals, particularly those without adequate hydration and/or effective cooling.

AVIATION

(06Z TAFS) Issued at 110 AM AST Tue Jun 9 2026

Mainly VFR conditions across all TAF sites. Expect the ESE winds around 10-16 kt with higher gusts and sea breeze after 09/13Z. VCSH possible across western Puerto Rico, affecting mainly TJPS and TJBQ between 09/18Z and 09/23Z.

MARINE

Issued at 110 AM AST Tue Jun 9 2026

The Azores high-pressure and a developing surface high in the western Atlantic will produce moderate east to east-southeast winds across regional waters, with occasional fresh winds causing choppy conditions, especially offshore. A tropical wave is forecast to reach the islands by Thursday, and This feature will likely increase shower and thunderstorm activity, with the greatest potential from Thursday afternoon to evening. Mariners should prepare for stronger winds and higher seas near thunderstorms.

BEACH FORECAST

Issued at 110 AM AST Tue Jun 9 2026

Generally, a low risk of rip currents will prevail today and tomorrow, Wednesday, due to weakening winds. However, life- threatening rip currents often occur in the vicinity of groins, jetties, reefs, and piers. Please exercise caution on our local beaches, as rip currents may still occur. A moderate risk of rip currents (life-threatening rip currents are possible in the surf zone) is forecast to return Thursday through the start of the next workweek, especially along the east and north-facing beaches in PR and the USVI.

FIRE WEATHER

Issued at 110 AM AST Tue Jun 9 2026

Drier-than-normal conditions will enhance the availability of burning fuels along the southern plains of PR and the USVI. The fire danger fro today is low, as conditions are present.

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.