Current Conditions | ||
Temp | ![]() | 1.6 C |
RH | ![]() | 96 % |
Wind | ![]() | E 9 mph |
Road | ![]() | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 754 FXHW60 PHFO 181957 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 957 AM HST Mon Jan 18 2021 .SYNOPSIS... A strong cold front looks to be stalling out near north Big Island this morning. Strong sustained north to northeasterly winds to around 30 mph gust up to 50 mph is starting to develop across the state and will continue to increase this afternoon. Added instability from an approaching upper level disturbance will enhance rainfall this afternoon through tonight, especially over Maui County and parts of the Big Island. Confidence is increasing for Flash Flooding to occur over select areas on Maui this afternoon into the evening. On Tuesday, the frontal moisture is expected to drift back toward the west and will likely bring another round of widespread rainfall to the western half of the state. Moderate to breezy easterly trade winds are forecast from Wednesday through the end of the week with periods of showers favoring windward and mountain areas. Trades could strengthen over the weekend. && .DISCUSSION... A cloudy, windy and rainy day for most areas across the state today. Forecast still remains on track for heavy rain to pick up over Maui County and parts of the Big Island this afternoon and persist through at least the first half of tonight. An upper level trough approaching the state, combined with the stalled frontal moisture over Maui and the Big Island will lead to the development of heavy showers and isolated thunderstorms this afternoon through tonight. The greatest threat for flash flooding looks to be over windward and mountain areas, where showers could anchor along the terrain. Select areas could see over 10 inches of rainfall throughout this event. So far, we have seen over 6 inches of rain on the mountain of Molokai from the Puu Alii rain gauge. Over 4 inches of rain has been reported by the West Wailuaiki gauge on Maui during the past 24 hours. A Flash Flood Watch remains in effect for Maui and the Big Island through Tuesday. A Flash Flood Watch also remains in effect for Oahu, and though the shower intensity will likely not be as strong as Maui County and the Big Island, we could see showers anchor over the Koolau mountain, which could potentially produce flash flooding. A Wind Advisory also remains in effect for the smaller islands due to the gusty northerly winds behind the front. Wind gusts of up to 50 mph is expected as the winds continue to strengthen during the day today. The strongest winds will occur over ridges and through valleys where winds can accelerate downslope. For tonight, the threat of flash flooding will continue over the Maui County and the Big Island through at least the first half of tonight. As we get closer to Tuesday morning, we could see the showers tapering off on the Big Island as the frontal moisture begins to shift back toward the west. This will bring another round of heavy showers to the western half of the state late tonight through Tuesday night. By Wednesday, most of the frontal moisture should be west of the state, and we should see our typical trade wind showers return across the state. Some lingering heavy showers will be possible over Kauai on Wednesday. Moderate to locally breezy trade wind weather will return during the second half of the week with trades potentially pick up to strong speeds over the weekend. && .AVIATION... A cold front will stall near the Big Island today. Widespread MVFR cigs/vsbys can be expected along and near the front, particularly in windward areas. Unsettled weather is expected to continue tonight over Maui County and the Big Island, and may spread back westward to windward sections of Oahu and Kauai. AIRMET Sierra remains in effect for mountain obscuration for windward sections of Kauai and Oahu, and for all of Molokai, Lanai and Maui. AIRMET Sierra may also be needed later today across the Big Island. AIRMET Tango remains in effect for low level turbulence over and downwind of the terrain from Kauai eastward to Maui. This AIRMET will likely continue through the day, and may need to be expanded to include the Big Island. AIRMET Zulu is in effect for moderate rime ice from Kauai eastward to Maui. Conditions may improve over Kauai and Oahu later today, but will likely hold over Maui County. This AIRMET may also need to be expanded to include the Big Island later today. && .MARINE... The overnight passage of a cold front is ushering in strong to near gale force north northeast winds in its wake. Frequent wind gusts to gale has warranted a Gale Warning that is in effect for the nearshore waters west of the Big Island until 6 PM HST. The front is expected to become near stationary over the Alenuihaha Channel today before slowly retrograding west Tuesday through Wednesday. The lower level convergence associated with this front weakening to a trough, along with forcing provided by its parent western upper level trough, will provide the necessary ingredients to maintain areawide showers, some becoming locally heavy, and isolated thunderstorms into mid week. Lingering moisture and this instability will likely keep maritime precipitation chances high through Thursday. The latest XL northwest swell will be arriving this morning and building surf back up to High Surf Warning (HSW) criteria today. This swell will be spreading down and across the Hawaiian Islands today and tonight, leading to another round of warning level surf to exposed north and west-facing shorelines. The HSW is in effect through 6 AM HST Tuesday. Buoy 51101 (180 nm NW of Kauai) has been consistently observing this latest northwest swell (16 feet, 14 second) since 4 AM HST. Although today's northwest swell is not as large as this past Saturday's near 20 foot swell, it will still create dangerous surf conditions. Surf will peak out in the 35 to 45 foot range along Kauai's north-facing shores, 30 to 40 feet along the north-facing shores of Oahu, Molokai and Maui this afternoon. This swell and subsequent surf will be trending down tonight through Tuesday. Surf is likely to lower to advisory levels for the north and west-facing shores of the smaller islands by late Tuesday morning and into the afternoon hours. Swell energy will also reach parts of the Big Island, but on a smaller scale latter today through Tuesday. A High Surf Advisory is in effect through Monday night for the exposed north and west-facing shores of the Big Island. Strong and gusty northeasterlies behind a cold front that is currently stalling out in the Alenuihaha Channel will ultimately impact wave shape and result in poorer surf quality. Strong to near gale force winds, along with this building northwest swell, has produced very rough, high sea conditions. A Small Craft Advisory (SCA) covers these greater than 10 foot significant seas across most windward and leeward nearshore Hawaiian waters. The SCA is currently in effect through 6 PM HST and will likely to be extended through at least tonight. && .HFO WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through Tuesday afternoon for Oahu-Molokai- Lanai-Kahoolawe-Maui-Big Island. Wind Advisory until 6 PM HST this evening for Niihau-Kauai-Oahu- Molokai-Lanai-Kahoolawe-Maui Windward West-Maui Leeward West- Maui Central Valley-Windward Haleakala-Leeward Haleakala. High Surf Warning until 6 AM HST Tuesday for Niihau-Kauai Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu Koolau-Olomana-Molokai-Maui Windward West-Maui Central Valley- Windward Haleakala. High Surf Advisory until 6 AM HST Tuesday for Kona-Big Island North and East-Kohala. Winter Weather Advisory from noon today to 6 AM HST Tuesday for Big Island Summits. Small Craft Advisory until 6 PM HST this evening for Big Island Windward Waters-Big Island Leeward Waters. Gale Warning until 6 PM HST this evening for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel- Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-Maui County Leeward Waters-Maalaea Bay- Pailolo Channel-Alenuihaha Channel. && $$ DISCUSSION...Kino AVIATION...Burke MARINE...Blood Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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