textproduct: San Juan

KEY MESSAGES

Issued at 159 PM AST Mon Oct 19 2026

* Slow-moving thunderstorms will maintain the potential for locally heavy rainfall and flooding through this afternoon, particularly across interior and western Puerto Rico. Stronger storms may produce frequent lightning and gusty winds.

* Dangerous coastal conditions will develop late tonight and continue through at least Wednesday morning. Breaking waves of 8 to 12 feet are expected from Rincon to Fajardo, with localized beach erosion and life-threatening rip currents along Atlantic- facing beaches of Puerto Rico and the U.S. Virgin Islands.

* A long- period north-northwesterly swell will produce hazardous seas across the Atlantic waters and exposed passages, peaking Tuesday and becoming northerly Wednesday.

* Rainfall coverage and flooding potential decrease Tuesday into Wednesday. Heat impacts will primarily affect heat-sensitive individuals without adequate cooling or hydration.

Short Term(This evening through Wednesday)

Issued at 159 PM AST Mon Oct 19 2026

Mostly clear skies early this morning gave way to showers downwind of the U.S. Virgin Islands and across portions of Puerto Rico by midmorning. Nearly stationary thunderstorms developed early this afternoon over western Puerto Rico, the southern slopes, and near the San Juan metro area as terrain effects and sea breeze convergence provided lift within weak steering flow. Rainfall totals of 12 inches, with locally higher amounts, prompted a Flash Flood Warning for portions of San Juan, Carolina, and Trujillo Alto. Winds remained light and variable with a weak east-southeast background flow. Hot and humid conditions primarily affected heat-sensitive individuals without adequate cooling or hydration.

This afternoon, daytime heating and local convergence will support showers and thunderstorms, particularly across interior and western Puerto Rico. Weak steering flow may favor slow-moving cells and repeated development, producing locally heavy rainfall and an elevated flooding threat across west-central and northwestern Puerto Rico. Urban and small stream flooding is possible, with isolated flash flooding where heavier rainfall persists. More localized rainfall impacts are possible across northeastern Puerto Rico and portions of the U.S. Virgin Islands. Thunderstorms may also affect adjacent waters, producing lightning and gusty winds. Activity should gradually diminish tonight, although occasional showers will remain possible over the local waters and windward areas.

On Tuesday, increasingly southerly flow aloft may shift afternoon convection toward northern Puerto Rico. The flooding threat should decrease and become more localized, mainly across northwestern and northeastern sections, while thunderstorms remain possible across the northern half of the island. Drier air arriving Tuesday night into Wednesday will further reduce shower coverage. The 06Z GFS indicates precipitable water values falling to around 1.31.5 inches Wednesday, accompanied by pronounced mid- level drying. This improvement will be brief, as moisture increases Wednesday night into Thursday, with precipitable water exceeding 2 inches.

Warm conditions will continue, particularly across northern coastal and urban areas. Heat impacts should primarily affect heat-sensitive individuals without adequate cooling or hydration, especially during the late morning and early afternoon.

Long Term(Thursday through Monday)

Issued at 130 AM AST Mon Oct 19 2026

No major changes to the long-term forecast. A southeast to southerly steering flow will persist across the region due to the interaction between a deep-layer low moving across the eastern CONUS and surface high pressure over the central Atlantic. Deep tropical moisture will return Thursday, with precipitable water values generally around or exceeding 2 inches through much of the period. Although a mid-level ridge is expected to build over the eastern Caribbean, abundant moisture, daytime heating, sea breeze convergence, and local topographic effects will continue to support scattered to numerous showers and thunderstorms. Passing showers will favor windward areas during the overnight and morning hours, followed by afternoon convection across interior Puerto Rico, spreading toward northern and western sections. Increasing steering winds Thursday through Saturday should favor more progressive convection. However, weakening winds late in the weekend into early next week may allow slower-moving or repeatedly developing thunderstorms, increasing localized rainfall accumulations. The main hazards will be lightning, urban and small-stream flooding, and isolated flash flooding where heavier rainfall persists, particularly during the afternoon hours. Meanwhile, the prevailing southeast to southerly flow will maintain hot and humid conditions, especially across northern coastal and urban areas of Puerto Rico. Heat impacts will primarily affect heat-sensitive individuals outdoors without effective cooling or adequate hydration during the late morning and early afternoon.

AVIATION

(18Z TAFS) Issued at 159 PM AST Mon Oct 19 2026

VFR conds should cont across most TAF sites throughout the fcst prd, though MVFR/IFR conds are likely across JSJ and JBQ due -TSRA/+TSRA near the sites through at least 19/21z. AMDs may be issue if required. By 19/22-23z, ESE-SE winds will weaken, becoming VRB and light, with VCSH across USVI and windward PR sites. Winds should strengthen btwn 7 - 12 kt around 20/13-14z. VCTS cannot be ruled out across PR terminals aftr 20/16z.

MARINE

Issued at 159 PM AST Mon Oct 19 2026

Low pressure and an associated frontal boundary over the western Atlantic will maintain a weak local pressure gradient, supporting gentle to moderate east to southeast winds through midweek. A long-period north-northwesterly swell will arrive late tonight, peak Tuesday, and become northerly by Wednesday, producing hazardous seas across the Atlantic waters and exposed passages. Showers and thunderstorms may produce locally gusty winds, lightning, and reduced visibility, particularly this afternoon and evening.

BEACH FORECAST

Issued at 159 PM AST Mon Oct 19 2026 A moderate risk of rip currents will continue this afternoon along Atlantic-facing beaches of Puerto Rico and the U.S. Virgin Islands. Conditions will deteriorate late tonight as a long-period north-northwesterly swell arrives, builds Tuesday, and becomes northerly by Wednesday.

A High Surf Advisory is in effect from 2 AM AST Tuesday through 6 PM AST, covering the area from Rincon to Fajardo. Dangerous breaking waves of 8 to 12 feet are expected, along with possible localized beach erosion. High Rip Current Risk is in effect along the Atlantic shoreline of Puerto Rico and the U.S. Virgin Islands from late tonight through at least Wednesday morning. Beachgoers should remain out of the water and away from exposed rocks and jetties.

Afternoon and evening thunderstorms may also bring lightning and gusty winds; seek shelter in a substantial building or enclosed vehicle when thunder is heard.

SJU WATCHES/WARNINGS/ADVISORIES

PR...High Rip Current Risk from late tonight through Wednesday morning for PRZ001-002-005-008-010-012.

High Surf Advisory from 2 AM to 6 PM AST Tuesday for PRZ001-002- 005-008-010.

VI...High Rip Current Risk from Tuesday evening through Wednesday morning for VIZ001.

AM...None.