000 FXCA62 TJSJ 250122 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 922 PM AST Fri Mar 24 2023 .UPDATE...Passing showers were increasing from the Anegada Passage and Atlantic waters during the evening hours. This will continue through the overnight hours as a weak trough moves from the east. Rainfall amounts should remain below half an inch in general, mostly across the U.S. Virgin Islands, and over portions of eastern and northern Puerto Rico. The 15-20 kt northeast trades could push showers further inland. Minimum temperatures should range from the mid 50s across the higher elevations to the low and mid 70s across coastal areas. && .AVIATION Update...Mainly VFR conditions expected to continue, however, quick passing showers may cause -RA/VCSH across the USVI terminals and TJSJ thru early Saturday morning. The 25/00z TJSJ sounding indicated NE winds up to 17 kt blo FL030. && .MARINE Update..Coastal buoys were indicating seas around 5 feet across the Atlantic waters, and up to 3 feet in the southern coastal waters. Northeast trades were between 12-18 kt. Wind- driven seas and a northerly swell will increase seas up to 7 feet across the offshore Atlantic waters later tonight. There is a high risk of rip currents along the north facing beaches of the islands through the weekend. && .PREV DISCUSSION... /issued 515 PM AST Fri Mar 24 2023/ SYNOPSIS...Overall fair weather conditions should prevail across the islands. Only a patch of shallow moisture will promote passing trade wind showers across windward sectors late tonight and into tomorrow morning. A Small Craft Advisory will be in effect for the offshore Atlantic waters from late tonight through at least late Sunday night. A High Risk of Rip Currents is in effect for the northwestern to northeastern beaches of Puerto Rico, as well as Culebra, and for beaches of the northern USVI. SHORT TERM...Tonight through Sunday... Current satellite derived precipitable water (PWAT) shows values of less than an inch, below normal for this time of the year, of columnar moisture over the eastern half of Puerto Rico, including Vieques and Culebra, and the USVI. An air mass with PWAT values of slightly above an inch is being observed over the western half of Puerto Rico and gradually moving over western waters. This available moisture, as well as northeasterly winds, sea breeze convergence and diurnal heating have promoted limited convective activity over southwestern Puerto Rico, this activity should gradually dissipate by around sunset. With the past frontal boundary staying and dissipating north of the region, any available moisture will be a result of patches of moisture filtering into the region. One patch of more humid air, with PWAT values near or at normal values, will arrive late tonight and into tomorrow, Saturday, morning. This will promote passing trade wind showers advecting over windward sectors during the morning hours and afternoon convection, due to diurnal and local effects, mainly over western/southwestern Puerto Rico. No flood threat is expected. A surface high pressure system spreading westward across the western Atlantic will promote easterly to northeasterly winds through the weekend. Any available moisture will be mostly restricted to the lower levels, a trade wind cap and drier air will continue in the mid to upper levels. Current model guidance indicates another patch of shallow moist air reaching the islands late Saturday into Sunday evening. Apart from these moisture patches, PWAT values will stay generally below an inch with overall fair weather conditions prevailing. LONG TERM...Monday through Friday... /FROM PREV DISCUSSION...issued at 452 AM AST Fri Mar 24 2023/ At this time, the mid-level high across the Caribbean Basin continues to be the dominating feature and will continue to be until Tuesday. The high-pressure system will maintain hostile conditions from 500 mb to 700 mb, limiting the potential for moderate to heavy rainfall activity. Therefore, by the beginning of the workweek, expect a mixture of sunny skies and cloudiness from time to time. Nevertheless, any rainfall activity across Puerto Rico and the U.S. Virgin Islands will be due to showers embedded within the trades or local effects. For the first part of the workweek, expect a more zonal wind flow. A short-wave trough will weaken the mid-level ridge by late Tuesday into Wednesday, changing the weather conditions. This weakening will allow more moisture to filter into the middle and upper levels, making the development of moderate and heavy rainfall likely. An approaching mid to upper-level trough from the northwest will increase instability for the second half of the workweek. Currently, PWAT values fluctuate around an inch or slightly less from Wednesday to Thursday. However, models suggest a higher increase by Friday as the trough amplifies over the northwestern Caribbean from Friday into the weekend. By the end of the workweek, the precipitable water content will be around 1.30 inches or higher. The latest models are showing Friday as the best day for organized convection. Nonetheless, it is too early to determine the impacts on Puerto Rico and the U.S. Virgin Islands. AVIATION...Mainly VFR conditions will prevail. Winds will remain out the ENE-NE at 15-20 kts with higher gusts and sea breeze variations, gradually decreasing and variable after 24/22Z and increasing to 15-20 kts after 25/12Z. Impact to operations will be limited, mainly at TJSJ and USVI terminals between 24/23Z and 25/13Z. MARINE...A surface high pressure over the Atlantic will continue to promote moderate to locally fresh trades across the regional waters. Therefore, choppy marine conditions with seas up to 6 feet and occasional higher seas will persist through this evening. Small Craft should exercise caution over the Atlantic waters, the offshore Caribbean Waters, the northwestern waters of Puerto Rico, and over the local passages. Marine conditions will further deteriorate by late tonight and into the weekend due to increasing winds and the arrival of a small northeasterly swell. A Small Craft Advisory will be in effect for the offshore Atlantic waters from late tonight through at least late Sunday night. A High Risk of Rip Currents is in effect for the northern beaches of Puerto Rico from Rincon and Aguada to northeastern municipalities as well as Culebra, and for beaches of the northern USVI. && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through Sunday afternoon for PRZ001-002- 005-008-010-012. VI...High Rip Current Risk through Sunday afternoon for VIZ001. AM...Small Craft Advisory from 2 AM Saturday to 2 AM AST Monday for AMZ711. && $$ DSR/GRS