textproduct: San Juan

KEY MESSAGES

Issued at 150 PM AST Sun Oct 18 2026

* Slow-moving thunderstorms may produce heavy rainfall locally and isolated urban and small-stream flooding this afternoon and Monday. Interior and northern Puerto Rico are favored today, with activity shifting to interior and western areas on Monday. * Stronger storms may produce frequent lightning and gusty winds. Heat will primarily affect heat-sensitive individuals outdoors without effective cooling or adequate hydration, especially during the late morning and early afternoon.

* Moderate rip current risk is expected today along exposed Atlantic-facing beaches of Puerto Rico and the U.S. Virgin Islands. A more energetic northwesterly swell arriving Monday evening will bring building seas, higher surf, and increasingly hazardous rip currents through midweek. The swell will peak Tuesday and shift to a northerly direction Wednesday.

Long Term(Wednesday through Sunday)

Issued at 235 AM AST Sun Oct 18 2026

Relatively drier conditions on Wednesday will transition into a wetter and more unsettled pattern Thursday through Sunday. The interaction between a surface high over the central Atlantic and a deep-layer low over the eastern CONUS will maintain a generally southeast to southerly wind flow across the region, with steering winds strengthening late Thursday into Saturday. Wednesday appears to be the driest day of the period, as model guidance suggests below-normal low- to mid-level moisture, with precipitable water values below 1.6 inches. Nevertheless, daytime heating and local effects may still support afternoon showers across portions of Puerto Rico.

A considerable increase in moisture is expected by Thursday as deep tropical moisture spreads across the northeastern Caribbean. Model guidance suggests precipitable water values exceeding 2.0 inches through much of the remainder of the period, occasionally approaching 2.4 inches, with periods of above-normal moisture. Increasing mid-level humidity, cooling temperatures aloft, and the proximity of a deep-layer trough will support a more favorable environment for deeper convection. Although a mid-level ridge may gradually build over the eastern Caribbean, abundant moisture and local effects should continue to favor showers and thunderstorms. An advective shower pattern is expected across windward sections of the islands, particularly during the nighttime and morning hours, followed by afternoon convection across the interior and western portions of Puerto Rico. Increasing steering winds late Thursday through Saturday should allow convection to become more progressive, although locally heavy rainfall may still result in urban and small-stream flooding, isolated flash flooding, and rises in river levels. By Sunday, steering winds may weaken again, potentially favoring slower-moving thunderstorms and greater localized rainfall accumulations.

Under the prevailing southeast to southerly flow, warmer than normal temperatures are likely, particularly across northern coastal and urban areas of Puerto Rico. Combined with abundant moisture, heat indices may exceed 100 degrees Fahrenheit, mainly during the late morning and early afternoon. Heat impacts may range from limited to elevated, particularly for individuals sensitive to heat, and heat products may be issued if conditions warrant.

AVIATION

(18Z TAFS) Issued at 150 PM AST Sun Oct 18 2026

TSRA/+TSRA across PR sites may reduce CIGs/VIS and lead to MVFR/IFR conds this aftn. Although JSJ, JPS, and JBQ have TEMPOs through at least 18/20-21z, AMDs will be issued if required. Aft 18/22-23z, VCSH could be expcd across E TAF sites, particularly across USVI sites. Meanwhile, ESE-SE winds will remain light and VRB through 19/12-14z, btwn 8 - 10kt. Aftn conv is also expcd aft 19/16z, with VCTS once again across PR terminals.

MARINE

Issued at 150 PM AST Sun Oct 18 2026

A surface low and its associated frontal boundary moving across the western Atlantic will maintain a weak local pressure gradient, supporting gentle to moderate east-southeast winds through early next week. Residual northerly swell will continue to subside today. A more energetic northwesterly swell will arrive Monday evening, peak Tuesday, and become northerly by Wednesday. This swell will produce building seas across the Atlantic waters and exposed passages, with elevated seas persisting through midweek. Thunderstorms may affect coastal waters, particularly in the afternoon and evening through at least Tuesday, producing locally gusty winds, lightning, and reduced visibility in heavy rain.

BEACH FORECAST

Issued at 150 PM AST Sun Oct 18 2026

A moderate risk of rip currents will continue this afternoon along the Atlantic-facing beaches of Puerto Rico and the U.S. Virgin Islands, particularly those exposed to northerly swell. Conditions will deteriorate Monday evening as a more energetic northwesterly swell arrives, building into Tuesday, and becoming northerly by Wednesday. Higher surf and an increased risk of life-threatening rip currents are expected along exposed beaches through midweek. Thunderstorms may affect beaches in the afternoon and evening, particularly today and Monday, bringing lightning and locally gusty winds. Beachgoers should seek shelter in a substantial building or enclosed vehicle when they hear thunder.

SJU WATCHES/WARNINGS/ADVISORIES

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