Current Conditions | ||
Temp | ![]() | -4.6 C |
RH | ![]() | 20 % |
Wind | ![]() | NNE 8 mph |
Road | ![]() | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 919 FXHW60 PHFO 260151 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 351 PM HST Thu Feb 25 2021 .SYNOPSIS... Breezy to locally windy trade winds will continue into the first half of next week. Rainfall will remain focused over windward slopes, but a disturbance aloft will enhance shower activity and may produce a few thunderstorms Friday through the weekend. && .DISCUSSION... An exceptionally strong 1047 mb surface high centered nearly 1600 miles north of the state is maintaining locally strong and gusty easterly trade winds. A Wind Advisory remains posted for portions of the Big Island and Maui, where sustained winds of around 30 mph have been measured at a handful of gages. A narrow upper level trough is building over the area from the east, eroding the inversion and leading to some instability. As a result, isolated heavy showers are flaring within a pocket of moisture currently affecting windward Oahu and Kauai, and although moisture is temporarily suppressed over the Big Island, a few showers are developing along leeward slopes along with a couple of freezing rain showers observed on the high summits. Winds will hold tonight and Friday as the atmosphere gradually destabilizes. The surface high will begin to drift eastward, but since winds will likely persist around current strength, we have extended the Wind Advisory through the day tomorrow. The upper level trough will settle over the islands, wiping out the inversion and producing instability. The GFS and ECMWF do not show sources of deep moisture that could help to trigger convection, but thunderstorms are a good bet for leeward Big Island slopes in the afternoon. Otherwise, showers will be focused over windward areas, with a few briefly passing over leeward areas on the strong trades. A breezy and somewhat wet and unstable trade wind pattern will prevail this weekend. Expect pockets of enhanced moisture moving in the trade wind flow to remain focused over windward areas, and deeper moisture developing near the Big Island and Maui could produce more widespread heavy showers and a few thunderstorms. The area with the highest risk of sustained heavy rainfall will likely be windward Big Island, though a Flash Flood Watch does not appear warranted at this time. The current run of breezy trades will persist into early next week. High pressure will dominate far north of the state, but the GFS and ECMWF continue to differ on some important details. The GFS shows the upper level trough overhead weakening, while the ECMWF suggests that this feature will be reinvigorated, leading to weaker trades and wetter conditions. The forecast favors the GFS, but confidence is low. && .AVIATION... Strong high pressure far north of the state is producing strong easterly trade winds across the area. AIRMET Tango remains in effect for low level mechanical turbulence for areas over and immediately south through west of mountains. This AIRMET will continue into the early morning hours. The strong winds are also causing low level wind shear near Kahului Airport. VFR conditions prevail across most of the area with brief periods of MVFR conditions over some windward locations in low clouds and showers. Expect these conditions to continue on through the overnight hours. && .MARINE... Strong high pressure NE and N of the islands will maintain strong to near gale force trade winds over and upstream of the islands into next week. A Small Craft Advisory (SCA) for all waters through the weekend will likely need to be extended further in time as winds and/or seas will continue to meet criteria early next week. Where winds are most accelerated, an ongoing Gale Warning for the Alenuihaha Channel has been extended through Friday, but a subtle decrease in wind speeds will likely allow the Gale Warning to be dropped over the weekend. Winds may increase again early next week as a new high builds N of the area. The strong trade winds extend well upstream of the islands, and are driving a well-developed (10-11 second period) wind swell toward the islands from the E. A High Surf Advisory for E facing shores will remain posted for the next several days. Elsewhere, surf will be below advisory levels, but several long-period NW swells are expected over the next week. Peaks in these swells can generally be expected tonight into Friday, Saturday night/Sunday, and Wednesday/Thursday, with the last swell expected to be the largest of the three. Some trade wind swell will wrap into exposed shores/reefs along N and S facing shores, and a small long-period S swell is also expected the next couple of days. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 AM HST Monday for Kauai Windward-Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward Haleakala-South Big Island-Big Island North and East. Wind Advisory until 6 PM HST Friday for Molokai-Kahoolawe-Maui Windward West-Maui Leeward West-Maui Central Valley-Windward Haleakala-Leeward Haleakala-South Big Island-Big Island North and East-Kohala-Big Island Interior. Small Craft Advisory until 6 PM HST Sunday 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-Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters. Gale Warning until 6 PM HST Friday for Alenuihaha Channel. && $$ DISCUSSION...Wroe AVIATION...Burke MARINE...Birchard Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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