256 FXCA62 TJSJ 100154 AFDSJU Area Forecast Discussion National Weather Service San Juan PR 954 PM AST Tue Oct 9 2018 .UPDATE...Passing showers will continue overnight across the regional waters. A few of these showers are expected to affect portions of the USVI and the eastern sections of Puerto Rico. Isolated thunderstorms across the Caribbean waters could briefly affect the southern coastal areas of Puerto Rico through at least midnight. Moderate trades will continue through Wednesday. Although drier air is expected on Wednesday, diurnally induced afternoon showers and thunderstorms are expected to develop over the interior and western sections of Puerto Rico. These thunderstorms could result in periods of lightning strikes and gusty winds as well as heavy downpours that will cause urban and small stream flooding. && .AVIATION...Mainly VFR conditions expected to prevail overnight across all the terminals. However, shra over the waters could move at times across the USVI terminals and TJSJ/TJPS, causing mainly VCSH and brief periods of -RA. Latest 10/00z TJSJ upper air sounding indicated 17-24 kt blo FL060. && .MARINE...No major change from previous discussion. Showers and isolated thunderstorms across the Caribbean waters could create locally higher waves and gusty winds overnight. && .PREV DISCUSSION... /issued 537 PM AST Tue Oct 9 2018/ SYNOPSIS...A surface high pressure ridge extends southwards across the northeastern Caribbean and will help to promote light to moderate easterly trade across the forecast area through Thursday. Tutt low and associated trough will continue to lift slightly north of the region through Thursday, while the weak mid to upper level ridge is expected to linger across the northeastern Caribbean. This pattern will support a slightly drier trend for the next couple of days as the local trade winds diminish and become more east-northeast. SHORT TERM...Rest of today through Thursday... A fairly moist environment along with local and diurnal effects and the moderate easterly trade winds, lead to afternoon showers and isolated thunderstorms across portions of the islands and coastal waters today. The heaviest rainfall was focused over parts of the central and west portions of Puerto Rico as well as over parts of northeast including the San Juan metro. The U.S. Virgin islands also experienced periods of moderate to locally heavy downpours during the afternoon. Expect shower activity over land areas to diminish just after sunset and into the evening hours leaving variably cloudy to partly cloudy skies. Wednesday through Thursday a somewhat drier airmass is expected to filter in across the region as the surface high pressure ridge is to build north of the region, and the winds become more east northeast thus limiting moisture transport. However, local and diurnal effects will lead to isolated to scattered afternoon convection each day, with the heaviest rainfall expected mainly over parts of the interior and west sections of Puerto Rico. Mostly isolated showers are forecast in and around the U.S. Virgin Islands with a mixture of sunshine and clouds each day. LONG TERM...Friday through Wednesday... The surface ridge of high pressure ridge is forecast to hold in place north of the region through Friday. The ridge is to then shift eastward into the central Atlantic by the upcoming weekend resulting in winds shifting and becoming more southeasterly. In the upper levels, the aforementioned Tutt is forecast to sink southwards across the region by the weekend resulting in increasingly unstable conditions aloft. A tropical wave is also forecast to enter the eastern Caribbean by late Saturday, then move across the region Sunday through Monday. This will bring deep tropical moisture and unsettled weather to the forecast area. The wave is expected to interact with the upper trough which will provide good ventilation and diffluence aloft supporting a very moist and and unstable weather pattern into early next week. During the entire period, small pockets of drier air will move through the area from time to time allowing occasional breaks in the early morning and afternoon convection each day. By Tuesday and Wednesday a drier airmass is so far forecast, as winds becomes more east northeast due to the surface high pressure ridge reestablishing north of the area. AVIATION...Isold SHRA will continue to move west across the area with some of them briefly affecting a few of the terminals. This could briefly create MVFR/IFR conditions...especially over TIST, TJSJ and later on over TJMZ and TJBQ terminals. SHRA/TSRA over western PR should diminish after 09/23Z. Isold/SCT SHRA could continue across USVI/Ern PR and so VCSH will be indicated over the eastern terminals. Low level winds will continue from the east southeast between 10 and 15 knots with sea breeze variations through 09/23z and land breezes overnight. MARINE... Seas will range from 4 to 6 feet across the Atlantic waters and Caribbean passages today. Therefore small craft operators are urged to exercise caution due to choppy seas. Elsewhere, seas are will range from 3 to 5 feet with winds ranging from 10 to 15 kts with higher gusts possible. Another surge of northerly swell associated with Leslie is expected to reach the local Atlantic waters by late Wednesday night or Thursday morning. There is a high rip current risk for the northern beaches of Puerto Rico and northern beaches of Culebra. && .PRELIMINARY POINT TEMPS/POPS... SJU 78 87 78 87 / 40 20 20 50 STT 81 85 81 86 / 30 20 20 50 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...High Rip Current Risk through Wednesday afternoon for Culebra- North Central-Northeast-Northwest-San Juan and Vicinity- Southeast-Western Interior. VI...None. AM...None. && $$ SHORT TERM...DS LONG TERM....RAM