Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
477 FXCA62 TJSJ 020844 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 444 AM AST Fri Oct 2 2026 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 440 AM AST Fri Oct 2 2026 - Showers and thunderstorms will become active again this afternoon, mainly across the interior and western to northwestern Puerto Rico. Passing showers will also continue across eastern Puerto Rico and the U.S. Virgin Islands, especially during the night and morning hours. - Locally heavy rainfall may cause urban and small-stream flooding, especially where repeated showers and thunderstorms occur. Areas with already elevated streamflows may be more vulnerable to additional rainfall. - Some thunderstorms may become strong through the weekend, producing frequent lightning and strong wind gusts. - Hot and humid conditions will continue, with the heat threat expected to increase Sunday into early next week, especially across coastal, urban, and lower-elevation areas. - A moderate rip current risk will continue along the north- and east-facing beaches of Puerto Rico and across portions of the U.S. Virgin Islands. && .Short Term(Today through Sunday)... Issued at 440 AM AST Fri Oct 2 2026 Lingering moisture associated with the surface-induced perturbation remained pooled over the Caribbean waters overnight. Under an east- southeast wind flow, this moisture supported an advective pattern of showers and isolated thunderstorms over the waters, with some of this activity occasionally moving into southeastern Puerto Rico and the U.S. Virgin Islands. Overall, rainfall accumulations were not substantial. Nevertheless, antecedent conditions remain a consideration today, particularly across eastern Puerto Rico, where streamflows may remain elevated following yesterday`s heavy rainfall. Elevated streamflows are also present across portions of northwestern Puerto Rico, where the highest probabilities for afternoon convection are expected today. Confidence remains high in another active afternoon across Puerto Rico. Moisture associated with the departing perturbation will remain sufficient, while a developing series of mid- to upper-level troughs will deepen over Hispaniola through Sunday. Although the strongest dynamics will remain west of the local area, their proximity will maintain colder temperatures aloft and increasingly favorable instability. For today, 500-mb temperatures are expected around -7 to -8 degrees Celsius, with 700-500 mb lapse rates steepening to nearly two standard deviations above climatological normals. Global ensemble guidance also shows relatively good agreement in maintaining sufficient moisture through the mid-levels today. The combination of this increasingly unstable environment with daytime heating, sea-breeze convergence, and local effects will favor afternoon showers and thunderstorms across the interior, spreading into western and northwestern Puerto Rico. Across the U.S. Virgin Islands, passing showers and isolated thunderstorms will remain possible, particularly within streamers, although the more widespread afternoon convection should remain focused over Puerto Rico. Locally heavy rainfall may result in urban and small-stream flooding, particularly where streamflows remain elevated. In addition, favorable instability aloft could result in near-severe thunderstorms capable of producing frequent lightning and locally strong wind gusts. On Saturday, the mid- to upper-level trough pattern will continue to deepen over Hispaniola, maintaining favorable conditions aloft for deep convection across the local area. Confidence remains fairly high in the potential for another active afternoon across Puerto Rico, although uncertainty increases regarding the distribution of moisture. Global ensembles remain in relatively good agreement in maintaining adequate moisture near 500 mb, while showing considerably more spread around 700 mb. Therefore, the coverage and persistence of convection will become more dependent on where sufficient moisture overlaps with local sea breeze convergence and local effects. Where this occurs, thunderstorms could become locally strong, producing heavy rainfall, frequent lightning, and gusty winds. By Sunday, the trough pattern will remain well established to the west while lower- to mid-level moisture becomes more variable. Confidence is therefore higher in the persistence of favorable instability aloft than in the exact coverage of showers and thunderstorms. Overall activity may become somewhat more conditional compared with Friday and Saturday, but locally strong thunderstorms will remain possible, particularly over western Puerto Rico. For the U.S. Virgin Islands and eastern Puerto Rico, passing showers across windward sections will continue during the night and early morning hours. During the afternoons, streamers may develop downwind of the islands and El Yunque, occasionally reaching the San Juan metro area. The heat threat will persist through the short-term period. Sufficient low-level moisture combined with warm temperatures will support locally high heat indices each day, particularly across urban and coastal areas and the lower-elevation valleys of Puerto Rico and the U.S. Virgin Islands, where at least a limited heat threat is expected. The potential for a more elevated heat threat increases on Sunday as low-level temperatures warm and atmospheric thickness values increase. Guidance brings 925 mb temperatures near the upper end of the climatological normal, which could support heat indices reaching Heat Advisory criteria in some areas if sufficient sunshine develops. Cloud cover and the timing of convection will remain important limiting factors. && .Long Term(Monday through Friday)... Issued at 440 AM AST Fri Oct 2 2026 Generally, the long-term period will be characterized by a seasonal weather pattern. A building high-pressure system over the central Atlantic will be the main weather feature for the long term period, enhancing an easterly wind flow from Monday through Tuesday. Under this pattern, the latest model guidance suggests seasonal precipitable water (PWAT). Despite the moisture lingering at the low levels, a mid-level ridge established over the region will promote stable conditions with warmer temperatures at 500 MB rounding between -6 and -4 degrees. That stability combined with some slightly drier mid-levels will inhibit some of the shower development during these days. Under these conditions, low-level lingering moisture, daytime heating, and local effects will be the primary drivers for shower and thunderstorm activity through Tuesday. A more southeasterly wind flow is forecast from Tuesday evening into Wednesday, as the broad building high pressure over the Central Atlantic deep into the area. An upcoming tropical wave and the associated moisture field will move south of the CWA, enhancing convection from late evening Tuesday into Wednesday. Although the bulk of the moisture associated with this wave is expected to remain over Caribbean waters, local effects, diurnal heating, and the available moisture will enhance strong convection along the islands. Due to the shift of winds to an east-southeasterly flow, the activity will shift more toward the interior and northwestern portions. Given the expected conditions, there is a chance to observe a limited to elevated flooding threat with the heaviest shower activity, especially on Tuesday and Wednesday. As a result, urban and small-stream flooding is possible over roadways and poorly drained areas, and flash flooding cannot be ruled out. In addition, an elevated heat risk from Monday is expected due to more stability anticipated and seasonal moisture levels. For those sensitive to the heat, staying hydrated and avoiding outdoor activities during peak heating hours is highly recommended. && .AVIATION... (06Z TAFS) Issued at 440 AM AST Fri Oct 2 2026 Mainly VFR conds are expected across all terminals through the fcst period. Passing -SHRA/VCSH will continue to affect TJSJ and the USVI terminals thru the morning hrs. Aft 02/17Z, SHRA/TSRA are expected to develop across interior and W/NW PR, with VCTS at TJBQ/TJPS and streamers potentially affecting TJSJ. Brief MVFR or lower conds are possible in heavier SHRA/TSRA, along with mtn obsc across the interior. E-ESE winds will increase aft 13Z to 10-15 kt, with gusts around 20-25 kt, before weakening again aft 22/23Z. && .MARINE... Issued at 440 AM AST Fri Oct 2 2026 Surface high pressure north of the region will maintain moderate to locally fresh easterly trade winds today, producing choppy conditions across the Atlantic and Caribbean waters and local passages. As the pressure gradient relaxes over the weekend, winds will ease to mainly moderate, keeping seas moderately choppy through Tuesday. Lingering moisture behind a departing disturbance will support showers and thunderstorms into the early weekend. Thunderstorms may produce locally hazardous conditions for small craft, including gusty winds, higher seas, lightning, and reduced visibility. && .BEACH FORECAST... Issued at 440 AM AST Fri Oct 2 2026 A moderate risk of rip currents will continue across most exposed north- and east-facing beaches of Puerto Rico and the U.S. Virgin Islands through much of the forecast period. Beachgoers should remain cautious into midweek, as dangerous rip currents can occur even when the risk is low, particularly near piers, jetties, groins, and rocky areas. Swim near a lifeguard and follow beach patrol guidance and posted warning flags. Afternoon thunderstorms may develop, especially across western and northwestern Puerto Rico. If you hear thunder, leave the water immediately and seek shelter inside a substantial building or enclosed vehicle. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM/AVIATION...CVB LONG TERM....JCP/LIS BEACH/MARINE...CAM