294 FXHW60 PHFO 100151 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 351 PM HST Tue Oct 9 2018 .SYNOPSIS... High pressure to the far northeast will maintain a moderate trade wind flow for another day, with showers focused over windward and mountain areas. The high will start to lift north and weaken tomorrow, which will weaken the winds through the end of the week. An approaching front will bring the chance for rain this weekend, and cooler temperatures by the end of the weekend. && .DISCUSSION... The morning analysis has the 1031 mb high about 1550 miles northeast of Honolulu, maintaining the trade winds over the state. Expecting the high and trades to stick around for another day, but will likely start to see trade winds easing tomorrow as the high starts to weaken and lift to the northeast. A band of clouds upstream of the islands will boost shower activity overnight mainly over windward locations, and looks like it'll reach the central islands around midnight. Afternoon clouds and showers over the west side of the Big Island have primarily been upslope, and expect that activity to die down after sunset. Have modified the PoPs and associated fields for this afternoon and evening to better reflect current conditions and the short term expectations. The weather gets more interesting during the second half of the week and through the weekend. A low far northwest of the islands is moving to the northeast bringing a surface trough towards the region. The models are in good agreement with a new surface low developing along this trough on Thursday, which will help to further disrupt our winds, leading to a lighter wind flow over the islands. This will likely lead to localized land and sea breezes, which will mean more clouds and showers over the interior of the islands during the afternoon. An upper level shortwave ahead of the surface feature could reach the western end of the chain Friday or Saturday. This could enhance shower activity over the islands, and could produce enough instability for some heavy shower activity. The global models have come into better agreement over the last 24 hours, so will be closely monitoring the next couple of runs to nail down timing. Heading into the weekend, this low will drop southward and bring a surface front closer to the islands. The front would reach the western islands Saturday and Sunday, and then stall out over the central islands Monday. The frontal passage will likely produce drier conditions than the shortwave, but the front will still have a noticeable impact on our weather. Dewpoints which were in the mid 70s recently making it feel muggy with the light winds have dropped to the upper 60s and low 70s. Behind the front this weekend, models show drier dewpoints pushing in, with the latest runs of the GFS and ECMWF showing dewpoints dropping into the low 60s Sunday night into Monday. Have made some modifications to the dewpoints at the end of the forecast period to be more in line with the latest guidance. Its still a ways out, but it looks like trade winds will make an appearance again by midweek. Modifications to the winds Monday onward were made to better reflect the winds behind the front switching over to a trade wind flow. && .AVIATION... High pressure centered far NE of the islands will maintain moderate to locally strong trade winds through at least tonight. The air mass has been unstable enough to negate the development of low-level turbulence over and downwind of the mountains, despite the breezy trades. Winds will diminish Wednesday through the end of this week, so AIRMET Tango will not be needed. The air mass across the island chain dried out some after the band of showers moved through last night, so there were far fewer showers overall today. This should continue through this evening, but forecast models are hinting at another band of showers to affect the islands sometime late tonight or Wednesday morning and may bring additional clouds and showers for brief periods of MVFR conditions. No other AIRMETs expected through Wednesday morning. && .MARINE... Moderate to locally strong trade winds will decrease tomorrow. A 1031 mb surface high sitting far northeast of the islands will gradually weaken on Wednesday and Thursday, leading to the decline in the trades. The Small Craft Advisory (SCA) in effect for the typically windy waters around the Big Island and Maui will likely be dropped by Wednesday morning. A developing trough near or over the islands will disrupt the trades on Friday, followed by a weak frontal passage that will usher in gentle to moderate northerly winds during the weekend. SCA strength winds are not expected to redevelop through early next week. East swell from distant Hurricane Sergio continues to slowly rise. PacIOOS buoys off of the Big Island, Maui, and Oahu suggest swell heights of 3 to 5 feet at 13 seconds, large enough to produce High Surf Advisory (HSA) level surf across east facing shores of those islands. The HSA has extended through Wednesday night based on Wavewatch III output. The east swell is expected to gradually decline Thursday and Friday. North and south facing shores will see surf through much of the week. A northwest swell is peaking at 4 to 6 feet 12 seconds today. This swell will decline over the next couple of days, followed by a smaller reinforcing swell on Thursday and Friday. A potentially larger north-northwest swell is due late Sunday and Monday. Small to moderate southwest swells will persist through much of the week, though a larger pulse tomorrow could produce south shore surf near the advisory level. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 AM HST Thursday for Oahu Koolau- Olomana-Molokai Windward-Maui Windward West-Windward Haleakala- South Big Island-Big Island North and East. Small Craft Advisory until 6 AM HST Wednesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...M Ballard AVIATION...TS MARINE...Wroe