textproduct: San Juan

KEY MESSAGES

Issued at 352 AM AST Sun Nov 8 2026

* Slow-moving thunderstorms will keep the potential for urban and small-stream flooding risk this afternoon, especially across interior and eastern Puerto Rico, including the San Juan metro area.

* Scattered showers and thunderstorms between the U.S. Virgin Islands waters could produce periods of brief, but heavy rainfall over land areas today.

* A northerly swell will maintain a high risk of life-threatening rip currents along exposed northern beaches of Puerto Rico and portions of Culebra through Monday. * By mid-week next week a stable weather pattern is expected to prevail across the region. However, diurnally induced afternoon thunderstorms are expected each day over the interior of PR.

Short Term(Today through Tuesday)

Issued at 352 AM AST Sun Nov 8 2026

A broad, decaying frontal boundary trailing across the western Atlantic will remain stalled well north of the region through Tuesday, while a surface high pressure builds into the central Atlantic. Between these systems, a plume of deep tropical moisture trailing the broad surface low over the central Atlantic will remain anchored over the northeastern Caribbean. Which is supporting convective bands over the Caribbean and Atlantic water under a deep southwesterly steering flow. Some of this activity is expected to move over land areas this morning, particularly across the U.S. Virgin Islands, and along western/southern coastal areas of Puerto Rico. At the upper levels, weak ridges building over the Caribbean basin and the tropical Atlantic will bring periods of dry air intrusion and somewhat stable condition. However, precipitable water (PWAT) content will fluctuate between 1.80 and 2.10 inches through the period, exceeding the 75th percentile of climatology. Sounding analysis and model guidance show saturated lower to middle levels, with 850-700 mb relative humidity averaging 70 to 80 percent, elevated equivalent potential temperatures, and near-normal lapse rates. Adding to the moist environment is an exceptionally weak wind field, with 925 mb winds remaining light to calm at 3 to 8 knots through Tuesday, falling near the climatological minimum in response to an approaching col area from the northwest.

That said, strong diurnal surface heating, sea breeze convergence, and local orographic lifting will interact with this moisture rich, weakly sheared environment each day. Expect nighttime and early morning showers to brush windward coastal areas of the islands, followed by strong convective development over the Cordillera Central and eastern municipalities during the afternoon. Because of light steering winds, convective cells will remain nearly stationary or drift slowly, significantly increasing local precipitation efficiency, with localized areas receiving over 2.00 inches. Therefore, the risk of urban and small-stream flooding, rapid rises along river tributaries, and localized mudslides across steep terrain will remain elevated each afternoon.

Boundary-layer temperatures at 925 mb will remain above normal, fluctuating between 21.5 and 22.5 degrees Celsius. With surface dewpoints holding in the mid-to-upper 70s, afternoon heat indices are forecast to reach 100 to 106 degrees Fahrenheit along coastal and urban areas of northern, western, and southern PR, as well as the U.S. Virgin Islands, before afternoon convection begins each day.

Long Term(Wednesday through Sunday)

Issued at 352 AM AST Sun Nov 8 2026

The long term period will be mainly characterized by variable conditions at the beginning, becoming slightly more stable by the end of the week. At the synoptic level, a surface high pressure will build across the western Atlantic by Wednesday, gradually shifting eastward into the central Atlantic during the remainder of the period. This will result in easterly winds by midweek, becoming east to southeasterly from Thursday through at least Saturday, before backing to the east once again on Sunday. Winds are expected to follow an increasing trend. Compared to previous days, when winds will remain light, they should increase to around 12 to 16 kt overall during the long-term period.

By Wednesday and Thursday, the latest model guidance suggests the influence of shortwave troughs near the Caribbean. Moisture content across the region is expected to remain near seasonal levels, with mean precipitable water values fluctuating between 1.7 and 1.9 inches. However, global models show some disagreement, with the GFS indicating higher values and the ECMWF showing lower values. Relative humidity in the 850 to 700 mb layer is expected to remain generally near seasonal levels, while the 700 to 500 mb layer should also maintain sufficient moisture to support cloud and precipitation development. The passage of shortwave troughs during this period could provide marginal dynamical support for upward motion. Combined with daytime heating and local effects, these features could contribute to periods of showers and possibly isolated thunderstorms, particularly during the afternoons across northern to northwestern portions of Puerto Rico. As a result, flooding will remain in the forecast across these areas (Level 1 of 4), indicating the potential for flooding in urban areas, along roads, and near small streams.

From Friday onward, moisture conditions are expected to remain relatively favorable, although a gradual decrease in mid-level moisture may occur as a ridge builds across the region. Precipitable water values are generally expected to remain near or below 1.9 inches, which is close to seasonal levels. However, the development of a mid-level ridge should promote greater atmospheric subsidence and potentially limit vertical development, despite the persistence of moisture in the lower levels. Additionally, models suggest a warming trend in 500 mb temperatures. Consequently, while isolated to scattered showers may continue, particularly due to local effects, precipitation activity could become more localized compared to Wednesday and Thursday.

Throughout the period, current model guidance suggests that 925 mb temperatures will remain near the 75th percentile or two standard deviations above normal, based on climatology for the month of November. Therefore, before rainfall develops, heat indices are expected to be elevated, primarily affecting individuals who are particularly sensitive to heat. Residents and visitors are encouraged to remain hydrated and continue monitoring weather conditions, as forecast updates and adjustments become available.

AVIATION

(06Z TAFS) Issued at 352 AM AST Sun Nov 8 2026

Mainly VFR conditions will prevail across the local terminals through most of the period. However, early morning TSRA developing in and around the USVI terminals and TJBQ will support mostly VCTS, with possible tempo MVFR conditions at TISX. Afternoon convection developing over the interior of PR will drift slowly and erratic toward coastal areas, producing mtn obscurations and VCTS at TJSJ/TJPS with tempo MVFR to brief IFR conds at TJSJ btw 08/18-21z. Surface winds will be light and variable, although a W-SW component is expected to continue through the fcst period.

MARINE

Issued at 352 AM AST Sun Nov 8 2026

A low-pressure northeast of the region will continue moving eastward over the next few days, while high pressure builds across the western Atlantic. Light to moderate westerly to southwesterly winds today will become variable tonight, then gradually shift to a more easterly direction early this week. A northerly to northeasterly swell will peak today through tonight, maintaining hazardous conditions near exposed Atlantic coastal waters. Although seas will remain below Small Craft Advisory criteria, the longer-period swell will produce locally rough conditions, particularly across the offshore Atlantic waters. The northeasterly swell will gradually subside on Monday, with improving marine conditions expected thereafter. Showers and isolated thunderstorms will remain possible across the regional waters through midweek.

BEACH FORECAST

Issued at 352 AM AST Sun Nov 8 2026

A northerly to northeasterly swell will peak today through tonight, producing breaking waves of 6 to 8 feet along exposed northern and northeastern beaches of Puerto Rico. Some of this swell energy will also reach the northwestern coastline, including the beaches of Rincon and Aguada, where a high risk of life-threatening rip currents is now in effect. A high rip current risk will also continue along other exposed northern and northeastern beaches of Puerto Rico, including Culebra, through at least Monday afternoon. Although swell energy will gradually subside on Monday, hazardous rip currents will likely persist as lingering swell continues to affect the region.

Elsewhere, a moderate rip current risk will persist along other exposed beaches, including portions of Vieques and the U.S. Virgin Islands. Thunderstorms will pose an additional hazard, with isolated thunderstorms possible through midweek. Avoid swimming at beaches with a high rip current risk. If thunder is heard, leave the beach and seek shelter in a substantial building or enclosed vehicle.

SJU WATCHES/WARNINGS/ADVISORIES

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

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