| Current Conditions | ||
| Temp |  | 8.2 C |
| RH | | 35 % |
| Wind | | W 12 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 899 FXHW60 PHFO 271959 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 959 AM HST Sat Nov 27 2021 .SYNOPSIS... Light winds and mostly dry weather will continue through the first half of Sunday. Trades will then quickly strengthen, potentially becoming locally strong by Sunday night as showers increase over windward and mauka areas. Occasional trade wind showers can be expected until winds once again diminish during the middle of next week. && .DISCUSSION... A corridor of weakly convergent boundary layer flow is in place from the Kauai channel to Oahu extending northeast. A result of easterly flow impinging on very light winds within a col, this area of weak low-level convergence will remain a focus for showers during the next 24 hours as it drifts westward. Around sunrise this morning, showers blossomed within this area, mainly over Oahu, and the forecast was updated accordingly. The latest radar imagery shows showers already diminishing in coverage and it has become clear that most of this morning's uptick in activity was a consequence of a gravity wave rolling through the area from the northwest. Nonetheless, the larger scale support for scattered showers will remain in place over Windward Oahu into this afternoon before shifting toward windward sections of Kauai overnight. The next to 36 to 48 hours will feature a transition away from the quiet and dry weather pattern that has dominated over the state recently. This transition will occur as energetic mid-latitude flow causes a closed low to develop and rapidly deepen near 150W Sunday into Sunday night. The response at the surface will be fairly impressive as a sharp trough develops east of the islands during that same time period. The subsequent tightening of the surface pressure gradient will result in trade winds quickly ramping up Sunday into late Sunday evening, then persisting in some fashion through Monday. Although the daytime hours on Sunday will again remain on the drier side of normal, the development of locally strong trades by early Sunday night will bring with it a greater coverage of trade wind showers. Frequent leeward penetration of showers can likewise be expected courtesy of the weakening inversion and stronger trades. As the upper low becomes established in the vicinity of the eastern islands, the aforementioned surface trough will begin to weaken as it pivots westward through the forecast area on Monday night. This could bring another quick hit of briefly stronger trades and robust trade wind showers. The latest modeling suggests that the deepest moisture will remain east of islands as it drawn northward during the middle of next week. Thus, as the gradient weakens and trades diminish beneath the lingering upper low during the mid-week period, the forecast focus will likely shift toward the Big Island where steepening mid-level lapse rates will result greater potential for a few afternoon thunderstorms over the interior slopes. At the same time, freezing levels will likely fall below summit level and, conditional on the exact location of the upper low, wind headlines may also be play for the Big Island summits. EC/GFS/GEM paint the same general picture of an elevated threat for more active weather in the extended range as renewed troughing potentially develops near or west of the islands during the latter half of next week. && .AVIATION... AIRMET Sierra is posted for mountain obscurations over windward sides of Oahu and Molokai due to some passing showers this morning. Elsewhere, VFR conditions prevail with light background winds. Sea breezes may bring some cloud build ups with isolated showers over the island interiors, particularly on Kauai and the Big Island where sunny skies prevail over most areas. && .MARINE... Trade winds will be on the lighter side through tonight as a weakening frontal boundary passes by to our north. An area of high pressure will then pass from west to east north of the area Sunday through Tuesday producing moderate to locally windy trade winds across the area. A Small Craft Advisory will likely be required for some areas especially the typically windy waters around Maui County and the Big Island. Winds will weaken Tuesday night and Wednesday as a low level trough begins to move in from the east. The weather may become more unsettled as well especially over the eastern waters. The current northwest swell will continue to lower through tonight. A reinforcing northwest swell will fill in on Sunday, peak Sunday night, then lower gradually Monday and Tuesday. Also, a small short period north swell will also move through the area Monday night and Tuesday likely causing conditions to be a bit disorganized. Another reinforcing northwest swell is then expected Wednesday and Thursday. Advisory level surf is not expected with any of these swells. A larger but rather short period north northwest swell may arrive around Friday. Surf along south facing shores will remain very small throughout the forecast period with only background swell energy from the Southern Hemisphere moving through the area. Some short period choppy surf is possible later in the week as winds turn southerly out ahead of a front. Short period choppy surf for east facing shores will gradually build beginning Sunday as trade winds increase over and upwind of the state. A downward trend is then expected beginning Wednesday as trade winds slowly diminish. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...JVC AVIATION...Foster MARINE...Burke Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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