Hurricane Season runs from June 1-November 30
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Area Forecast Discussion (AFD)
629 FXCA62 TJSJ 061756 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 156 PM AST Tue Oct 6 2026 ...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST... .KEY MESSAGES... Issued at 156 PM AST Tue Oct 6 2026 - Shower and thunderstorm activity is expected this afternoon, mainly over interior to western Puerto Rico, bringing a limited to moderate flood risk. - A Heat Advisory remains in effect from 10AM to 4PM, with the highest risk along coastal zones, lowlands, interior valleys and urban areas. Anyone sensitive to extreme heat is encouraged to stay hydrated and limit outdoor activities during peak daytime heating hours. - Increasing moisture from a tropical wave passing south of the islands will promote a wetter, more active weather pattern on Wednesday, with lingering moisture supporting an active afternoon on Thursday. - A moderate risk of rip currents will persist through Thursday across north- and east-facing beaches of the islands. && .Short Term(This evening through Thursday)... Issued at 156 PM AST Tue Oct 6 2026 A fair morning prevailed across the islands. Mostly clear skies, seasonal moisture content, and variable to calm winds have promoted high heat index values, up to 110 over coastal areas, thus a Heat Advisory remains in effect from 10 AM to 4 PM. This afternoon, streamers from the USVI, Vieques, and Culebra reached eastern portions of Puerto Rico, but activity was brief, with the rest of the CWA experiencing mostly fair weather. Persistent drier mid- levels should limit deep convection today; however, low-level moisture, daytime heating, and local effects will still be enough to trigger localized shower and thunderstorm activity. Driven by a more easterly flow induced by the tropical wave crossing the Windward Islands, this activity will focus primarily over interior and western PR. Meanwhile, streamers from the USVI, Vieques, Culebra, and El Yunque could reach the San Juan metro area as well as northern and eastern PR. From tonight into tomorrow, the bulk of the tropical wave moisture field will remain south of the region. However, a shift to a more east-southeasterly wind patternfavored by a mid-level ridge north of the CWAwill drag some of that moisture toward the islands, pushing PWAT values up to 2.00 inches. This will deepen moisture through the mid-levels of the atmospheric column and setup a more active Wednesday. Frequent showers may begin overnight, followed by a variable weather pattern during the morning hours, particularly over the USVI, Vieques, Culebra, and eastern PR. Widespread shower and thunderstorm activity is expected Wednesday afternoon under the ESE flow, with the heaviest rain occurring across northern, eastern, and western PR. By Thursday, lingering moisture will enhance a more seasonal pattern, with 03 km east-southeasterly wind flow directing the strongest shower and thunderstorm activity mainly toward northern and northwestern PR. Consequently, a limited to moderate excessive rainfall risk remains one of the primary hazards throughout this period. The heaviest showers may lead to urban, small stream, and localized flash flooding, with the highest flood threat peaking on Wednesday as rainfall coverage expands. Additionally, the strongest thunderstorms could produce frequent lightning and brief strong wind gusts. Furthermore, heat will remain a major concernespecially on Thursday, as clearing cloud cover will allow daytime heating to increase. For those sensitive to these events, staying hydrated and limiting outdoor activities during peak daytime heating hours is strongly recommended. && .Long Term(Friday through next Monday)... Issued at 156 PM AST Tue Oct 6 2026 A weak mid-to-upper-level ridge is expected to build just north of the region on Friday. This ridge will promote mid-level warming, suppress lapse rates, and introduce drier air aloft, significantly capping widespread convective development. On Friday, the 500 mb temperatures are forecast to increase to near -4C, roughly two standard deviations above normal for early October, while precipitable water values temporarily drop to around 1.50 inches. Despite this overall drying trend, intense daytime heating, along with local sea breeze convergence, will still trigger localized afternoon showers across the western interior of PR. A similar pattern will continue on Saturday, with a slight influx of low-level moisture supporting brief, passing trade wind showers over windward areas during the overnight and early in the morning, followed by typical afternoon shower development over the interior and western PR. By Sunday and into early next week, global model guidance suggests a more unstable atmosphere, as an upper-level trough or cut-off low digs near or just southeast of the islands. This will promote anomalously low geopotential heights and cold temperatures aloft, with 500 mb temperatures dropping sharply to near -8C by Sunday and Monday, and steeper mid-level lapse rates. Concurrently, broad-scale velocity potential guidance indicates a highly favorable environment for upper-level divergence over the Caribbean basin, strongly supporting deep, organized convection across the islands. Alongside these upper-level dynamics, a surge of deep tropical moisture will pool across the area, driving seasonal precipitable water values of near 2.00 inches. Given the highly unstable environment, saturated atmospheric column, and excellent upper-level venting, widespread showers and strong thunderstorms are anticipated across the forecast area. The primary impacts will be an elevated risk of urban and small-stream flooding, localized flash flooding, and frequent lightning, particularly over the mountain ranges of PR during the afternoon hours. However, the USVI could also see periods of heavy rainfall. Light low-level steering flow will keep showers slow-moving through Monday, supporting the increasing flood threat. By Tuesday, trade winds are expected to strengthen as a surface high pressure builds north of the region, increasing low-level winds around 20 knots; however, they will turn more southeast, and 925 mb temps could rise well above seasonal levels and increase the heat threat once again across the islands. && .AVIATION... (18Z TAFS) Issued at 156 PM AST Tue Oct 6 2026 Afternoon SHRA/TSRA will spread across interior to W-SW PR thru 06/22-23Z, with brief MVFR/IFR possible at TJPS. SHRA/TSRA associated with an approaching tropical wave may also bring brief MVFR/IFR to TISX, with PROB30 as activity spreads N-NW. Local convection diminishes quickly this eve, but tropical-wave SHRA/TSRA will continue at exposed terminals overnight. TJBQ should remain mostly VCSH, though brief SHRA/TSRA cannot be ruled out. Locally reduced VSBY, LTG, and gusty/VRB winds possible. ESE winds 10-15 kt, becoming light/VRB overnight. && .MARINE... Issued at 156 PM AST Tue Oct 6 2026 Moderate easterly winds will prevail tonight, strengthening somewhat Wednesday as high pressure builds over the western Atlantic and a tropical wave moves across the region. Seas will generally range from 2 to 4 feet, occasionally up to 5 feet, with a small northerly swell spreading across the Atlantic waters. Afternoon showers and thunderstorms will affect portions of the coastal waters through this evening, while additional showers and thunderstorms associated with the tropical wave will spread across the local waters tonight and continue through Wednesday night into Thursday. && .BEACH FORECAST... Issued at 156 PM AST Tue Oct 6 2026 A moderate risk of rip currents will continue along the north- and east-facing beaches of Puerto Rico, as well as Vieques, Culebra, and the U.S. Virgin Islands, while a low risk prevails elsewhere. A small northerly swell will continue spreading across the local Atlantic waters tonight. An approaching tropical wave will increase shower and thunderstorm activity overnight into Wednesday, resulting in an increased lightning risk at area beaches. Locally gusty winds are also possible near thunderstorms. Increased shower and thunderstorm activity will persist into Thursday as the wave crosses the region. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...Heat Advisory until 4 PM AST this afternoon for PRZ001>013. VI...Heat Advisory until 4 PM AST this afternoon for VIZ001-002. AM...None. && $$ EVE...DSR/KML MID...YZR/RVM DAY...ICP/MRR/JCP
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