textproduct: San Juan

KEY MESSAGES

Issued at 145 AM AST Tue Oct 20 2026

* Dangerous surf, hazardous seas, and life-threatening rip currents will affect the Atlantic waters, exposed passages, and north-facing beaches of Puerto Rico, Culebra, and the northern U.S. Virgin Islands through Wednesday, with conditions gradually improving thereafter.

* Afternoon thunderstorms may produce lightning, locally heavy rainfall, and urban or small-stream flooding across northern Puerto Rico today. Activity should decrease Wednesday before a surge of tropical moisture brings more widespread showers and renewed flooding concerns Thursday into the weekend.

* Wednesday will likely be the warmest day of the period, with heat primarily affecting individuals extremely sensitive to heat, especially those outdoors without effective cooling or adequate hydration.

Short Term(Today through Thursday)

Issued at 145 AM AST Tue Oct 20 2026

A weak pressure gradient between a frontal boundary over the western Atlantic and subtropical high pressure to the east will maintain weak southeast to southerly flow through the lower and middle levels, with winds generally between 5 and 10 knots, occasionally reaching 15 knots. Similar to yesterday, showers over the surrounding waters will move into windward areas of Puerto Rico and the U.S. Virgin Islands overnight into the early morning hours, gradually diminishing as daytime heating shifts convective development inland. Despite below-normal moisture, sea breeze convergence and local terrain effects will favor slow-moving afternoon showers and thunderstorms across the northern half of Puerto Rico, mainly from the interior toward north-central sections and the San Juan metro area.

Wednesday will bring less active weather, with precipitable water values decreasing to around 1.4 to 1.5 inches. Greater sunshine and weak southerly flow will likely make it the warmest day of the period, with reduced afternoon convection. However, global models agree on a surge of tropical moisture beginning Wednesday evening, sustained by southerly flow through Thursday and into the weekend. Increasing upper-level moisture will favor expanding cloud cover Thursday morning, potentially limiting daytime heating and favoring more widespread passing showers. By Thursday afternoon, deep tropical moisture should cover the forecast area, with precipitable water values increasing to around 2.2 to 2.3 inches. This will begin a wetter pattern through Saturday, followed by gradual drying beginning Sunday evening.

Regarding hazards, afternoon thunderstorms today could produce frequent lightning, ponding of water on roads and poorly drained areas, and localized urban and small-stream flooding, particularly across northern Puerto Rico. These impacts should become less likely Wednesday as shower and thunderstorm coverage decreases. Meanwhile, warmer temperatures and greater sunshine will primarily affect individuals extremely sensitive to heat, especially those outdoors without effective cooling or adequate hydration. By Thursday, increasing tropical moisture will favor more widespread showers and locally heavy rainfall, potentially resulting in flooding of urban areas, roads, small streams, and poorly drained locations, with a low chance of isolated flash flooding. Extensive cloud cover could limit thunderstorm development, while breaks in the clouds and local convergence may favor heavier convection and lightning. The areas most susceptible to flooding will depend on where persistent or repeated rainfall develops, with their location potentially shifting as forecast guidance evolves.

Long Term(Friday through Tuesday)

Issued at 145 AM AST Tue Oct 20 2026

No major changes were introduced to the long-term forecast. Wet and unsettled weather conditions are expected across Puerto Rico and the U.S. Virgin Islands through much of the weekend, with the greatest potential for widespread showers and thunderstorms Friday into Saturday, followed by gradually improving conditions beginning Sunday.

A southeast to southerly steering flow will persist across the region due to the interaction between a deep-layer low moving across the eastern United States and surface high pressure over the central Atlantic. This pattern will allow deep tropical moisture to spread across the region, with precipitable water values around or exceeding 2 inches. Latest model guidance also indicates anomalously high mid-level relative humidity, favoring enhanced shower and thunderstorm development and locally heavy rainfall. Despite a building mid-level ridge over the eastern Caribbean, daytime heating, sea breeze convergence, and local topographic effects will support passing showers across windward areas during the overnight and morning hours, followed by scattered to numerous afternoon thunderstorms across interior, northern, and western Puerto Rico. Unsettled conditions will likely continue into Saturday, although increasing steering winds should favor more progressive showers and thunderstorms. By Sunday, a gradual reduction in atmospheric moisture is expected, leading to decreasing shower coverage. However, weakening steering winds late in the weekend could allow thunderstorms to move more slowly, increasing the potential for localized rainfall accumulations. The main hazards Friday through the weekend will include lightning, urban and small-stream flooding, and isolated flash flooding, particularly where repeated or persistent heavy showers occur. Meanwhile, persistent southeast to southerly winds will maintain hot and humid conditions, with the greatest heat impacts expected across northern coastal and urban areas, particularly for individuals spending extended periods outdoors without adequate cooling or hydration.

A more noticeable improvement in weather conditions is forecast for Monday into Tuesday as drier air spreads through the atmospheric column and increasing subsidence associated with the mid-level ridge limits convective development. This should favor a drier and more stable weather pattern across the region early next week.

AVIATION

(06Z TAFS) Issued at 145 AM AST Tue Oct 20 2026

Passing SHRA may produce brief MVFR cigs/vsbys across USVI terminals and TJSJ through 20/13-14Z. Aftn SHRA/TSRA may bring MVFR/IFR conds to TJSJ after 20/15-16Z and TJBQ after 20/16-17Z, mainly due to reduced vsbys in heavier SHRA/TSRA and locally low cigs. VCTS also possible near TJPS and USVI terminals, with activity diminishing after 20/22Z. Sfc winds light/VRB overnight, becoming ESE-SE at 5-10 kt after 20/13Z, with sea breeze variations and locally gusty winds near TSRA.

MARINE

Issued at 145 AM AST Tue Oct 20 2026

A weak pressure gradient between a frontal boundary over the western Atlantic and high pressure to the east will maintain gentle to moderate east to southeast winds through midweek. Despite the relatively light winds, a significant long-period north-northwesterly swell is expected to peak today before becoming more northerly Wednesday. Seas near 6 feet across the Atlantic waters and exposed passages will warrant caution for small craft operators, with conditions gradually improving as the swell subsides. Meanwhile, increasing tropical moisture Thursday into the weekend may favor more widespread showers and thunderstorms, potentially bringing lightning, locally gusty winds, and reduced visibility over the waters.

BEACH FORECAST

Issued at 145 AM AST Tue Oct 20 2026

A significant long-period north-northwesterly swell is expected to peak today, with breaking waves of 8 to 12 feet possible along exposed northern and northwestern beaches of Puerto Rico, from Rincon to Fajardo. A High Surf Advisory remains in effect through 6 PM AST this evening, with dangerous swimming conditions and possible localized beach and dune erosion. High tide around 3 to 4 PM AST, reaching approximately 1.5 feet along northern Puerto Rico, Vieques, and Culebra, may enhance wave runup and localized beach erosion along exposed shorelines. Large waves may also wash over exposed rocks and jetties.

A High Rip Current Risk will continue through Wednesday afternoon along these beaches and the north-facing beaches of Culebra. The risk is also expected to increase to high along the north-facing beaches of St. Thomas, St. John, and adjacent islands beginning this evening through Wednesday afternoon. Although surf heights should gradually decrease Wednesday as the swell becomes more northerly and subsides, life-threatening rip currents will remain a concern.

Beachgoers should remain out of the water at affected beaches and away from exposed rocks and jetties. Improving surf conditions later in the week may be accompanied by increasing showers and thunderstorms, potentially bringing lightning and gusty winds to coastal areas. Seek shelter in a substantial building or enclosed vehicle when thunder is heard. For additional information, refer to the latest Coastal Hazard Message (CFWSJU).

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk through Wednesday afternoon for PRZ001-002- 005-008-010-012.

High Surf Advisory until 6 PM AST this evening for PRZ001-002- 005-008-010.

VI...High Rip Current Risk from this evening through Wednesday afternoon for VIZ001.

AM...None.