103 FXUS66 KMTR 092338 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 438 PM PDT Tue Oct 9 2018 .SYNOPSIS...Onshore flow will continue through Wednesday with cooler temperatures. Weak offshore flow will then likely develop late in the week, resulting in warmer and drier conditions from Friday on through the weekend. Dry weather conditions will persist through at least the middle of next week. && .DISCUSSION...as of 03:10 PM PDT Tuesday...Afternoon visible satellite imagery shows coastal clouds lingering along the Marin and Sonoma County coastlines and nosing in through the Golden Gate. This is a result of onshore flow dominating the Bay Area region. Onshore flow will continue through the night as a broad deep trough persists over the Intermountain West. A shortwave is forecast to ride down the western flank of this trough tonight, bringing a pulse of NNE winds to the North Bay Mountains. Some peak in Napa County could gust into the 40 mph range overnight with an outside chance of reaching 50 mph in brief gusts. Humidity at the time is expected to be in the 25% range. At this time there is no Red Flag Warning in place. The Fire Weather Forecast highlights the gusty winds, but conditions are not expected to meet RFW criteria. Either way, diligence and vigilance is always encouraged when conditions are even remotely close to carrying fires. Going for a tale of two halves, drizzle will be an issue along the immediate coast tonight. With the shortwave we'll be looking at a deepening marine layer and should be able to squeeze out abundant moisture from the onshore flow. As such, the afternoon package did expand the reach of drizzle all the way up the Sonoma coast and down to Monterey. Temps across the region will remain seasonable through tomorrow before the shortwave along the broad trough pinches off along the California coast. This will induce some weak offshore flow and warming conditions. Therefore, look for a warming and drying trend for the second half of the week. Overall the forecast remains on track with limited changes. Confidence remain generally high in the pattern for the week with a cutoff low along the coast for the second half of the week. If along the coast or the immediate shoreline, be ready for some wet roadways, otherwise enjoy the fair fall weather. && .AVIATION...as of 04:37 PM Tuesday...For 03z tafs. Satellite imagery shows low clouds over the waters and along the Sonoma and Marin coastline with passing high clouds overhead. Stratus is expected to penetrate further inland tonight than was seen yesterday. LIFR to MVFR cigs are forecast for most coastal terminals with the exception of KLVK and KSJC. Some offshore winds will be possible aloft overnight at KLVK and especially KOAK with relatively calm winds at the surface. Some patchy coastal drizzle will also be possible overnight. Vicinity of KSFO...VFR. Some patchy stratus will be possible late tonight into early tomorrow morning. Satellite will be monitored and taf will be updated as needed. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Currently VFR. An early return of LIFR to IFR cigs is expected for KMRY and KSNS lasting into late tomorrow morning. Exact timing on the return is uncertain, but current thinking is between 02Z-05Z. Satellite will be monitored and tafs will be amended as needed. && .FIRE WEATHER...As of 3:30 AM PDT Tuesday...The general trend through Wednesday is for increasing onshore flow and a deeper marine layer across the district, and thus cooling temperatures and better nighttime humidity recoveries in the hills. However, the exception is possible localized dry and gusty north winds in the North Bay Mountains late tonight and Wednesday morning. Strongest winds are expected to be across the higher hills of eastern and northern Napa County, as well as extreme northeast Sonoma County. In these areas wind gusts of up to 35 mph are possible late tonight through Wednesday morning. Because this is expected to be a short-duration and localized offshore wind event, Red Flag Warnings are not currently anticipated. Will headline local gusty offshore winds in the Fire Weather Forecast. More widespread light offshore flow is forecast to develop late in the week which will result in warm and dry conditions across most of the district from Friday into the weekend. && .MARINE...as of 02:39 PM PDT Tuesday...Split flow across the waters through the next few days with stronger northwest winds in the northern and outer waters and southerly winds along the coast. Occasional to infrequent gale force gusts are possible in the outer waters north of Point Reyes through this evening. Mixed swell with small to locally moderate northwest and southerly swells. Southerly swell peaks later this week due to Hurricane Sergio west of Southern Baja. && .BEACHES...Tropical storm Sergio will bring moderate period and height swell to the Central California and Bay Area coastlines beginning Thursday morning. Exposed south facing beaches will be at highest risk for building surf. Some breakers may reach as high as 10 feet with 10 to 20 minute lulls between sets. All beaches will experience an increase in rip current activity during the second half of the week as this swell arrives and transits the area. Therefore, a Beach Hazards Statement has been issued from early Thursday morning through late Friday afternoon. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm SCA...Pt Arena to Pt Reyes 0-10 nm until 4 AM SCA...SF Bay until 11 PM && $$ PUBLIC FORECAST: BFG AVIATION: AS MARINE: DRP FIRE WEATHER: Dykema BEACHES: BFG Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea