Current Conditions | ||
Temp | ![]() | 1.9 C |
RH | ![]() | 29 % |
Wind | ![]() | N 12 mph |
Road | ![]() | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 989 FXHW60 PHFO 170658 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 858 PM HST Sat Jan 16 2021 .SYNOPSIS... A cool and wet pattern is on tap for the islands during the first half of the coming week. This comes about as a front moves down the island chain Sunday night, then stalling around Maui and the Big Island between Monday and Tuesday. The front, or trough, is then slated to drift back to Oahu and Kauai between Tuesday night and Wednesday. The front will have good support aloft from an upper level disturbance, resulting in heavy showers and a slight chance of a thunderstorm. Strong trade winds will accompany the passage of the front, along with some cooler temperatures. && .DISCUSSION... A change in the weather is forthcoming. A cold front with strong trade winds and cooler temperatures behind it will move down the main Hawaiian Islands, starting with Kauai late Sunday afternoon, Oahu early Sunday evening, Maui County during the rest of Sunday night. The front is expected to come to a rest near Upolu Point Big Island and the Alenuihaha Channel early Monday. Both the new GFS model run and old ECMWF, are in pretty good agreement, although the ECMWF has the front further west over Maui County. The models have the front, or trough by this time, to drift back west to Oahu on Tuesday, then Kauai Tuesday evening. As the front or trough moves back west, the winds will become easterly and lighter. As noted, the temperatures will be cooler on Monday and Tuesday, lowering from a daytime high of 84 degrees, to the upper 70's and near 80. It could be possibly cooler, in the mid 70's on Monday, with all the clouds and showers. The rough weather is likely to occur between Monday and Tuesday, that is when the front is slated to be in the vicinity of Maui/Big Island, with increasing upper level support. The upper trough will have a pool of cold air of about minus 16 degrees F at 18k feet. Normally, the temperature at that height is minus 8 degrees F. In the coming hours, we will be assessing the need for some land based advisories, such as a Flash Flood Watch, beginning as early as Sunday night. The summits of the Big Island may receive some wintry weather as well, which may warrant a Winter Storm Watch. The strong trade winds will may warrant a Wind Advisory as well. On Wednesday afternoon, the ex-front, now trough, will be west of Kauai, and moving further away from the islands. The weather will be somewhat better with less showers during the second half of next week, but the air mass will still be unstable due to a trough aloft. Trade winds will be in the moderate to strong range across the region. Currently, light south to southeast winds are present across most of the smaller islands. A shower is noted just off Diamond Head, and scattered showers along Oahu's windward shoreline. We do expect isolated showers to pop up here and there the rest of tonight across the smaller islands. Isolated showers have just sprung up along parts of the Big Island's leeward coast, from north of the airport to around Kawaihae/Kamuela. These showers will dissipate by midnight or drift into the adjacent waters due to a developing land breeze. The Hilo, Puna, parts of the Kau district may get a shower or two overnight, carried ashore by a trade wind flow. && .AVIATION... Winds have diminished considerably in advance of a cold front approaching Kauai from the northwest. Mostly clear skies and weak winds will allow land breezes to develop in favored areas tonight as VFR prevails. Light wind will then emerge out of the southwest as the front approaches during Sunday with continued VFR and a low coverage of poorly organized shower activity for Oahu through Big Island. Nothing more than brief MVFR is expected within the heaviest showers for these locations. Deepening moisture will bring the potential for increasing showers to Kauai by late Sunday morning or early Sunday afternoon with increasing probability for widespread showers after about 00z/2pm HST. Prevailing MVFR and widespread showers, some locally heavy, can be expected over Kauai as front moves across the island around 03z/5pm or shortly thereafter. In addition to the onset of more widespread rainfall, the arrival of the front will be marked by a sharp transition to gusty northerly winds. No AIRMETs in effect. && .MARINE... In summary, expect giant surf to continue tonight, then gradually decline tomorrow, with another giant swell Sunday night into Monday. A potent cold front will move over most of the island chain late Sunday night into Monday, and then stall over the islands Monday and Tuesday, bringing the potential for heavy showers and thunderstorms. Strong to near gale-force N to NE winds will develop over most waters as the front passes, potentially persisting into Tuesday. A High Surf Warning remains in effect for exposed N and W facing shores as the largest NW swell of the winter season continues to propagate through island waters. The peak of the swell has already occurred in Kauai and Oahu waters, and will likely peak in Maui County and Big Island waters overnight. Buoy data indicate that surf may drop below warning-levels from NW to SE during the day Sunday, but another giant swell building Sunday night and Monday will once again bring warning-level surf, but peak surf heights are expected to be lower than today's swell. Very strong N to NE winds will destroy any chances of quality surf along N facing shores with this swell. A High Surf Advisory remains in effect for exposed N and W facing shores of the Big Island, as most of the swell's energy is blocked from upstream islands. A Small Craft Advisory remains in effect for all waters except Maalaea Bay, as the NW swell continues to produce seas greater than 10 feet. A Marine Weather Statement is highlighting the potential for surges and significant wave action in and near exposed harbors, although the potential will be gradually diminishing through Sunday. Due to the period and size of the NW swell, some (increasingly reduced) swell may wrap into select S and E facing shores. A vigorous cold front will rapidly approach the islands from the NW tonight and tomorrow, leading to a period of light to moderate S to SW winds, with some pre-frontal showers developing within this flow through Sunday. The front will move over Kauai Sunday evening, and Oahu by midnight before stalling over the central portion of the island chain early Monday, bringing some heavy showers and the potential for thunderstorms. Strong to near gale- force N to NE winds will follow the front, and a Gale Watch is in effect for waters from the Alenuihaha Channel westward starting Sunday night, due to the tight gradient between a strong high to the NW and the lower pressure along the stalled front (that eventually transitions to a trough). A developing sharp trough aloft on Monday will likely invigorate the lingering moisture through Wednesday as it drifts westward, keeping the potential for heavy showers and thunderstorms. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Warning until 6 PM HST Sunday 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 PM HST Sunday for Kona-Big Island North and East-Kohala. Small Craft Advisory until 6 PM HST Sunday for all Hawaiian waters except Maalaea Bay- Gale Watch from Sunday evening through late Monday night 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. && $$ H Lau/JVC/Birchard Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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