Current Conditions | ||
Temp | ![]() | 2.7 C |
RH | ![]() | 80 % |
Wind | ![]() | S 11 mph |
Road | ![]() | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 807 FXHW60 PHFO 180208 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 408 PM HST Sun Jan 17 2021 .SYNOPSIS... A vigorous front will move down the island chain tonight, then stall around Maui and the Big Island between Monday and Tuesday. Behind the front, we will see strong northerly winds of 20 to 30 mph with stronger gusts. The combination of strong northerly winds, and an upper level low aloft, will bring the risk of Flash Flooding to parts of Oahu, Maui County and the Big Island. The greatest risk will be along windward and mountain areas, especially on Maui Monday afternoon and Monday night. Moderate to strong easterly trade winds return to the region during the second half of the week with a bit of a wet flavor. && .DISCUSSION... The leading edge of a vigorous cold front is now moving through Kauai and is expected to move through Oahu and Maui County later tonight. Numerous impacts are expected with this front, including the potential of flash flooding and strong northerly winds behind the front. A Flash Flood Watch has been expanded to include the Big Island with this forecast package. Confidence is increasing for flash flooding Monday into Monday night especially around windward areas of Maui County and the Big Island. Latest model guidance are in fairly good agreement with the front stalling between Maui and the Big Island on Monday. The combination of the strong northerly winds and an upper level low aloft will enhance precipitation and will allow rainfall to anchor over the terrain. Confidence is increasing for select areas to receive over 10 inches of rainfall during this event. The most likely areas to see heavy rain will be over windward Maui and the Hamakua Coast on the Big Island between Monday afternoon and Monday night. Also due to the strong northerly winds expected behind the front, a Wind Advisory has been issued for the smaller islands with sustained winds of 20 to 30 mph with gusts of over 45 mph expected. Although the front looks to dissipate on Tuesday, moisture associated with the front will continue to linger across the state and is expected to slowly drift westward through Wednesday. The strong northerly winds should taper off by then, and breezy trades should return by the middle of the week. A trade wind pattern is expected for the second half of the week but due to lingering moisture, we will likely see a more of a wet trade wind pattern. && .AVIATION... A front near Kauai will move down the island chain through tonight. While clouds and showers are associated with the frontal cloud band, showery prefrontal cloud areas are affecting some of the islands now. TAF sites will begin to experience MVFR conditions from time to time, at least across the smaller islands, as the frontal cloud band passes by. AIRMET Sierra for tempo mountain obscuration above 2500 ft is in effect for the western islands and may need to be expanded eastward later tonight and into Monday. The arrival of the cold front is expected around 06z/8pm HST for Oahu and around 15z/5am HST for Maui and will be marked by a greater coverage of showers, some locally heavy, followed by an abrupt shift to gusty northerly winds. && .MARINE... A cold front is passing into the nearshore Kauai waters late this afternoon and is timed to make it into Oahu's nearshore waters late this evening. The front will slow along its southeastward progression and will likely stall out over the central islands going into early Monday. The approach, passage and eventual stalling of this frontal boundary will produce a few days of showers, some locally heavy, and isolated thunderstorms across the Hawaiian waters. The western upper trough across the waters surrounding Kauai, along with the weak convergence along the near stationary surface boundary, will be the impetus to maintaining higher shower and thunderstorm chances through mid week. The High Surf Warning (HSW) has been extended in time and is now in effect through 6 AM Tuesday morning for all smaller island exposed north and west-facing shorelines. Despite this afternoon into evening's brief lowering of surf to near or below warning level criteria, the HSW will remain in effect to account for the next large northwest swell's arrival during the overnight Monday morning hours. This powerful 14 to 16 foot, near 14 second period northwest swell will push surf heights back to over warning level thresholds along all smaller island north and west-facing shores. Peak surf heights during the day Monday into early Tuesday are not expected to be quite as high as they were during this most recent weekend XL surf event. A High Surf Advisory (HSA) is in effect for the north and west-facing Big Island shorelines as surf peaks out around HSA criteria tomorrow afternoon. Strong north to northeast winds in association with this early week cold front will result in lesser quality wave shapes during the passage of the highest swell. While these most recent swell directions of around 330 degrees are not traditionally favorable for significant impacts within both Kahului and Hilo Bay Harbors (as with a more north swell direction), there is a slight chance that there could be some minor harbor surge impacts. A Gale Warning is in effect for the Alenuihaha Channel and westward waters as strong post-frontal north to northeast winds will frequently gust to greater than gale force. Heightened passing northwest swells, along with very rough seas in the wake of the cold front, will produce greater than 10 foot significant seas across most nearshore waters through Tuesday night. A Small Craft Advisory (SCA) for high seas remains in effect for the windward Big Island waters tonight. This SCA will be expanded to include the leeward Big Island waters tomorrow. && .HFO WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through Tuesday afternoon for Oahu-Molokai- Lanai-Kahoolawe-Maui. Wind Advisory until 6 PM HST Monday 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. Flash Flood Watch from Monday morning through Tuesday afternoon for Big Island. High Surf Advisory until 6 AM HST Tuesday for Kona-Big Island North and East-Kohala. Small Craft Advisory from 6 AM to 6 PM HST Monday for Big Island Leeward Waters. Small Craft Advisory until 6 PM HST Monday for Big Island Windward Waters. Gale Warning until 6 PM HST Monday 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...Powell MARINE...Blood Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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