Current Conditions | ||
Temp | ![]() | -0.4 C |
RH | ![]() | 100 % |
Wind | ![]() | NE 12 mph |
Road | ![]() | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 966 FXHW60 PHFO 190231 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 408 PM HST Mon Jan 18 2021 .SYNOPSIS... The frontal moisture has stalled over Maui County and parts of the Big Island this afternoon and is producing heavy rain across the eastern half of the state. The heavy rain will continue overnight and gradually shift westward towards Oahu and Kauai Tuesday and Tuesday night. The strong north to northeasterly winds is starting to fill in over Maui County this afternoon and is expected to gradually decrease across the state by late tonight into Tuesday. 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 are expected to strengthen to strong speeds over the weekend. && .DISCUSSION... A Flash Flood Warning remains in effect for the island of Molokai and parts of Maui this afternoon. Rainfall intensities have picked up since this morning and we are seeing widespread rain with rates of 1 to 2 inches per hour with locally up to 4 inches per hour across Maui County and parts of Big Island this afternoon. Over the past 24 hours, we have seen over 12 inches of rain reported on the Puu Alii gauge on Molokai and over 5 inches on Maui. These amounts are expected to continue to increase tonight. Further west on Oahu and Kauai, we have seen the strong north winds fill in behind the front with several weather stations reporting wind gusts of 50 mph. For rest of this afternoon and tonight, we are expecting stronger wind gusts to move into Maui County this afternoon and evening. The Wind Advisory has been extended through tonight, but we should see the winds gradually taper off during the second half of tonight. Heavy rain will continue overnight across Maui County and the threat of flash flooding will begin to expand further east into east Maui and north Big Island this afternoon and evening. By late tonight, the frontal moisture is expected to gradually shift westward and the threat of heavy rain should begin to decrease over Big Island and increase over Oahu into Tuesday morning and over Kauai by Tuesday night. Although heavy showers will be possible Tuesday, we are expecting these showers to be moving and not staying stationary like today. Thus the threat for flash flooding will decrease, but still remain possible on Tuesday. 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 is stalled between Maui and the Big Island. Widespread MVFR cigs/vsbys can be expected along and near the front, particularly in windward areas. Unsettled weather is expected to continue tonight across portions of the state especially Maui County. AIRMET Sierra remains in effect for mountain obscuration for windward sections of Kauai, Oahu and the Big Island, and for all of Molokai, Lanai and Maui. 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 overnight hours. 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 Sunday 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 have warranted a continued Gale Warning (GLW) through the overnight Tuesday morning hours. The GLW is in effect for the nearshore waters west of the Big Island until 6 AM HST Tuesday. The front has become stationary near the Alenuihaha Channel and will slowly retrograde west 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 scattered to isolated thunderstorms into mid week. Lingering moisture within this instability will likely keep maritime precipitation chances high through Thursday. The latest XL northwest swell is passing through and spreading down across the Hawaiian Islands. This will be build surf back up to High Surf Warning (HSW) criteria along smaller island north and west- facing shorelines tonight through Tuesday morning. 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 and has increased swell heights above model guidance this afternoon (15-20 feet, 14-16 second energy). The PacIOOS Waimea buoy's swell observations have jumped up over the past few hours with 20 second energy focused at 310 degrees. Early Tuesday morning surf will peak out in the dangerous 30 to 40 foot range along Kauai, Oahu, Molokai and Maui's north-facing shores...20 to near 30 feet along the west- facing shores of Kauai, Oahu and Molokai due to the more westerly component to these swells wrapping around northwestern shores. This swell and subsequent surf will be trending down through the day Tuesday. Swell direction will be veering more northerly into Tuesday and this will lessen Tuesday's surf heights along western-exposed shores. Surf will lower to advisory levels for the north and west- facing shores of the smaller islands by Tuesday afternoon. Swell energy will also reach parts of the Big Island, but on a smaller scale later tonight through Tuesday. A High Surf Advisory is in effect through tonight for the exposed north and west-facing shores of the Big Island. Strong and gusty northeasterlies behind a cold front that is currently stalled out near the Alenuihaha Channel will ultimately impact wave shape. This will result in poor surf quality with this latest winter northwest swell event. Eastern shore surf will stay up through mid week. This is primarily due to post-frontal strong to near gale force northeast winds pushing more wind wave swell onto eastern-exposed shorelines. Strong to near gale force winds, along with this building northwest swell, has produced very rough, high sea conditions. A GLW covers all windward and leeward Hawaiian Island waters. The exception is the ongoing Small Craft Advisory (SCA) that covers the greater than 10 foot significant seas across the east and southeastern windward waters surrounding the Big Island. The SCA is currently in effect through 6 AM HST Tuesday and may need to be extended into Tuesday afternoon as northwestern swells subside through the morning hours. && .HFO WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through Tuesday afternoon for Oahu-Molokai- Lanai-Kahoolawe-Maui-Big Island. Wind Advisory until 6 AM HST Tuesday 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 until 6 AM HST Tuesday for Big Island Summits. Gale Warning until 6 AM HST Tuesday 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-Big Island Leeward Waters. Small Craft Advisory until 6 AM HST Tuesday for Big Island Windward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Kino AVIATION...Burke MARINE...Blood Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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