Area Forecast Discussion
Issued by NWS San Juan, PR
Issued by NWS San Juan, PR
654 FXCA62 TJSJ 210819 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 419 AM AST Fri Jun 21 2024 .SYNOPSIS... A typical weather pattern with passing windward showers and active afternoon convection over the interior and western Puerto Rico is to be expected through the next week. A series of tropical waves will approach the area starting early next week, furthering this pattern. && .SHORT TERM...Today through Sunday... Showery conditions has been observed across the islands during the night hours, but rainfall estimates from the NEXRAD in Cayey did not show any significant accumulations. Recent infrared satellite imagery shows some lingering high clouds coming from the west, from a developing system over Mexico and Central America. Close to home, satellite-derived precipitable water shows a patch of enhanced moisture approaching the islands from the southeast. The high resolution and global models show an increase in shower activity for the region today, first moving over portions of eastern Puerto Rico and the Virgin Islands, and reaching the west in the afternoon hours. Conditions aloft are not really favorable for strong thunderstorms, but strong heating should be enough to fire up some thunderstorms this afternoon. The risk for flooding will be elevated for the west, and limited for the rest of the area. A surface to mid level high pressure will drive the trade winds from the east southeast this weekend, with speeds at around 15 to 20 knots today through Sunday. In this flow, induced patches of moisture will reach the islands at times. The Galvez-Davison Index show a better chance for thunderstorms in the afternoon for the interior and western Puerto Rico. There will be some Saharan dust at the low levels too, turning skies hazy, but also enhancing the lightning activity each afternoon. Temperatures will remain above normal these days too, with highs reaching the low 90s at coastal areas, and lows close to 80. Heat indices will be elevated too, with a limited heat risk anticipated. && .LONG TERM...Monday through Friday... A robust surface high stretched across the central Atlantic will maintain a pattern of trade wind showers followed by afternoon convection across the islands throughout the week. Plenty of moisture remains over the area with constantly high precipitable water values which will yield in an abundance of showers at times. On Monday, a tropical wave begins to move across the area, bringing unstable conditions across the the lower levels that will aid in thunderstorm development across the area. Generally relatively high pressure will remain across the mid to upper- levels during this time, however with the instability caused by the tropical wave and a continued east to southeasterly flow, rain may be persistent and heavy a few time throughout this period. The movement of an area of low pressure north of the region by mid-week will help maintain high precipitable water values as easterly flow pushes a moist airmass over the region. Afternoon convection due to local effects and diurnal heating will play a big role in allowing thunderstorms to form, with western Puerto Rico most likely to receive the bulk of rain and the greatest risk of excessive rainfall. && .AVIATION... (06Z TAFs) Mainly VFR conditions expected to prevail through the forecast period. SHRA will continue across the region, impacting the USVI terminals and TJSJ through the day. Widespread SHRA and isolated TSRA expected after 15Z, reaching also TJPS and TJBQ. Periods of reduced VIS and low ceilings are anticipated, as well as mountain obscuration for the Cordillera Central. Winds will be out of the E at 14-18 kts, with gusts around 25 kts from 13-22z. && .MARINE... A surface high pressure over the central Atlantic will promote moderate to locally fresh easterly winds through the rest of the week. Trade wind showers will move across the regional waters from time to time. The next tropical wave will approach the local islands by the beginning of the next workweek. .BEACH FORECAST... A moderate risk of rip currents is present for the northern, eastern and southwestern exposed beaches of Puerto Rico, Vieques, Culebra and St. Croix. Remember, life-threatening rip currents are possible in the surf zone. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. && $$ SHORT TERM...ERG LONG TERM....RC