Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
111 FXHW60 PHFO 110214 CCA AFDHFO Area Forecast Discussion...CORRECTED National Weather Service Honolulu HI 414 PM HST Sat Aug 10 2024 .SYNOPSIS... Gentle trades will allow more wind protected area`s local breezes to dominant the wind regime for the reminder of 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 the areal coverage of trade wind showers. Precipitation will generally favor better exposed windward areas and mauka slopes during the overnight hours with a few showers reaching leeward communities. && .DISCUSSION... Today`s 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. Radar depicts lessened shower coverage through the afternoon with the bulk of the showers traveling just upstream of Oahu and Maui County. As these isolated weak showers come onshore they will occasionally stick 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 1,000 miles northwest of Kauai has caused the pressure gradient back to a strengthening 1032 mb surface high centered about 1,600 miles northeast of Oahu to ease a touch. The result has been lighter regional trade flow the past few days. Localized gentle land and sea breezes have ruled many communities` late week diurnal wind patterns in the absence of stronger large scale flow. These breezes have produced more efficient cloud growth and shower development over better wind- protected leeward and interior areas such as Big Island`s Kona regions. As surface high pressure gradually strengthens and drifts westward north of the state the next couple of days, the 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 may lead to a subtly less stable environment. Bands of higher mid-level moisture advection within stronger trades Sunday (and then again from Tuesday onward) is a hopeful signal that a more wet pattern is coming that may provide brief relief from the dryness. Remnant moisture from the once T.C. Emilia in the East Pacific may move through late Wednesday into early Thursday and this boost in moisture could produce more areawide rain. While thicker clouds and higher shower frequency will still favor windward and mauka areas in this typical summertime trade wind regime, occasional showers may make it over the ridgetops and briefly wetten leeward communities. A drier air mass is expected to follow at the end of the upcoming work week. && .AVIATION... Moderate trade winds will strengthen into Sunday, delivering low clouds and periodic brief showers to windward areas, producing isolated MVFR CIG. No AIRMETs are in effect, and none are anticipated overnight. Increased trade wind speeds bring the potential for low-level turbulence downwind of the terrain on Sunday. && .MARINE... Building high pressure north of the state will result in trade winds strengthening slightly tonight to become moderate to locally strong. As a result, a Small Craft Advisory will be in effect for the typically windier waters of Maui County and the Big Island beginning at 6 PM HST this evening through early Tuesday. 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. The current small south swell (13-14 seconds) will hold through tonight and then gradually 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. As trades increase both upstream and locally, expect east facing surf to gradually build Sunday through the first half of next week. A small boost in surf along east facing shores will also be possible early next week from former Tropical Cyclone Emilia. && .FIRE WEATHER... Recent spotty brushfires are 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 early July. The majority of the islands are under moderate drought conditions with southern Maui (east of Maalaea Bay) experiencing extreme drought. Recent afternoon minimum relative humidities have consistently been falling below 50% during the heat of the day. One of the fire weather indices such as the Keetch-Byram Drought Index (KDBI) is a tool that is used to better determine the fire weather threat. This index has been on the rise and will likely exceed fire weather threat thresholds by the end of August. This index employs such factors as locally drying fuels, strong winds and lower relative humidities that, in combination, all lead to enhancing the fire weather threat within a drought. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Tuesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION/FIRE...Blood AVIATION...Birchard MARINE...Vaughan