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Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
694 FXHW60 PHFO 102000 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 1000 AM HST Sat Aug 10 2024 .SYNOPSIS... Gentle trades will allow more wind protected area`s local breezes to dominant the wind regime through the day. Trades will strengthen to more breezy magnitudes from Sunday through late next week. Periodic bands of higher moisture moving in from the east will increase trade wind shower areal coverage. Precipitation will generally favor better exposed windward areas and mauka slopes during the overnight hours with a few showers reaching leeward communities. && .DISCUSSION... Morning visible satellite imagery shows mainly clear to partly sunny skies across most lower elevations...partly to mostly cloudy skies over much of the state`s elevated terrain. A slightly more active radar in relation to Friday morning. Greater areal coverage of showers traveling across the windward waters and developing in the downstream Big Island plume...isolated weak showers sticking to the smaller island windward-facing slopes. Central Pacific upper level ridging remains weakened by the influence of troughing located northwest of the islands. The associated surface cold front approximately 950 miles northwest of Kauai has caused the pressure gradient back to the 1029 mb surface high centered 1,700 miles northeast of Oahu to ease a touch these past few days. The result has been lighter regional trade flow. Localized gentle land and sea breezes have ruled many communities` diurnal wind patterns in the absence of this stronger large scale flow. These breezes will create more efficient cloud growth and shower development over better wind-protected leeward and interior areas (i.e., leeward Big Island). As surface high pressure gradually strengthens and drifts westward north of the state early next week, the resultant tighter pressure gradient back toward the islands will result in a return of more areawide breezy trades. There are slightly higher probabilities that next week will be a touch more wet in relation to this past dry week. Weak upper level troughing begins to develop northeast of the area into mid week. Lowering heights will lead to slightly higher vertical temperature inversions and less stable atmospheric profiles. Higher mid-level moisture advection within stronger trades Sunday and again from Tuesday onward signals a subtly more wet pattern within a less stable environment. Remnant moisture from the once was once T.S. Emilia in the East Pacific may move through Thursday. While thicker clouds and higher shower frequency will still favor windward and mauka areas in typical trade wind weather behavior, occasional showers may make it over the ridgetops and briefly wetten leeward communities. A drier air mass is expected to follow for the end of the upcoming work week. && .AVIATION... Light to moderate trade winds will strenghten slightly tonight and Sunday, delivering low clouds and periodic brief showers to windward areas. Developing sea breezes will fuel a few clouds and showers over leeward coasts and slopes this afternoon, mainly on the Big Island and Maui. Isolated MVFR CIG can be expected. No AIRMETs are in effect, and none are anticipated today. && .MARINE... Building high pressure north of the state will result in the moderate to locally fresh trade winds today strengthening to locally strong levels tonight. To account for this uptick in trades tonight, a Small Craft Advisory will go into effect for the typically windier waters of Maui county and the Big Island. Winds may weaken slightly around the middle of the week as a weak trough moves over the state from the east. Otherwise, little variation is expected. A small south swell (14 seconds) will peak today slightly above the summer average, then slowly decline Sunday and Monday. Several small south swells may move through the state next week, keeping small surf along south facing shores. A tiny pulse from the north northwest will keep tiny ripples along north facing shores through the rest of the weekend. Small, below average surf along east facing shores will persist through the rest of today. As trades increase both upstream and locally, expect east facing surf to gradually build Sunday into early next week. A small boost in east facing shore surf is also possible early next week from former Tropical Cyclone Emilia. && .FIRE WEATHER... Recent spotty brushfires is a reminder of the recently dry statewide conditions. Below normal rainfall and higher seasonable temperatures have resulted in an increase of drought coverage and intensity since the July 4th holiday. The majority of the islands are under moderate drought with southern Maui (east of Maalaea Bay) experiencing extreme drought. One of the fire weather indices such as the Keetch-Byram Drought Index (KDBI) that helps determine the fire weather threat is on a consistent rise. Of course, other factors such as locally dry fuels, high winds and lower relative humidities all lead to enhancing the fire weather threat within drought. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory from 6 PM this evening to 6 AM HST Tuesday for Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Blood AVIATION...Birchard MARINE...Vaughan