Current Conditions | ||
Temp | ![]() | -2.6 C |
RH | ![]() | 30 % |
Wind | ![]() | WNW 0 mph |
Road | ![]() | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 122 FXHW60 PHFO 070153 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 353 PM HST Sat Mar 6 2021 .SYNOPSIS... A high to the north will maintain breezy to locally strong trade winds for the next several days. Continued heavy showers are expected to move ashore over Kauai through tonight, with passing windward showers elsewhere. Starting early Monday, deep moisture will move in from the southeast, first affecting the the Big Island, then spreading to all islands later Monday and Tuesday. This increase in moisture will bring the potential for heavy rainfall that will likely remain for most of next week. && .DISCUSSION... In summary, breezy to locally strong trade winds will prevail for the next several days. Wet trade wind weather is expected over Oahu and Kauai tonight, while windward portions of Maui County and the Big Island will see a few showers as well. The focus for increased showers, and potentially heavy rainfall, is expected to shift to the Big Island starting early Monday as a trough develops near the islands. The threat of widespread rainfall will spread to all islands later Monday and Tuesday, with the potential for wet weather persisting for most of next week. Most showers will focus over windward areas, but there is a chance for increased rainfall over leeward areas if the low-level trough sharpens near the islands. Surface high pressure consolidating far N of the islands will support breezy to locally strong trade winds for the next couple of days, with the wind forecast becoming increasingly uncertain thereafter as a surface trough may or may not sharpen near the islands. Moisture associated with a dissipated front will continue to move into Kauai and Oahu from the E overnight, while an E-W oriented trough aloft near Kauai acts to enhance this moisture. Although moving rather quickly, heavy showers repeatedly moving in from the E have led to saturated grounds on Kauai. A Flash Flood Watch (FFA) is in effect for Kauai through tonight as high- resolution model guidance indicates that showers will persist, if not intensify. This moisture is expected to gradually clear Oahu this evening and Kauai by Sunday morning, leading to a fairly typical distribution of trade showers statewide on Sunday. On Sunday night, a low aloft is expected to develop within the trough aloft just W of the islands. This will lead to a realignment of the flow aloft, further destabilizing the island atmosphere while drawing moisture NW over the area. As this moisture moves over the Big Island, guidance depicts a surface trough developing near the islands, with the associated low-level moisture convergence bringing an increased potential for heavy rain (and winter weather to the Big Island Summits). Since the threat on the Big Island appears to start early Monday, it was decided to hold off on a Winter Weather Watch/Flash Flood Watch for the Big Island at this time, but these may need to be posted on Sunday. As the trough moves W (and potentially sharpens) later Monday and Tuesday, the potential for heavy showers will spread to all islands while the low aloft persists. Trade winds will likely focus most of the rainfall over windward areas, but if winds turn toward the S or SE (per latest GFS), potential for significant leeward rainfall will increase. Depending on when/where/if the trough sharpens, winds could become locally strong. The lingering low aloft will prevent a significant drying trend until next weekend. && .AVIATION... VFR conditions prevail at all TAF sites with some brief periods of MVFR conditions conditions occurring at PHLI and PHTO in low clouds and shra. Expect these conditions to continue into the overnight hours. AIRMET Sierra is currently in effect for Kauai due to mountain obscuration. Conditions are expected to improve overnight. They will likely be brief periods of MVFR conditions elsewhere along windward slopes through the overnight hours as low clouds interact with island terrain. AIRMET Tango is currently in effect over and immediately south thru west of mountain ranges on Kauai due to low level mechanical turbulence. Winds may diminish a bit during the overnight hours. && .MARINE... Large, strong high pressure located about 1,000 miles north of the islands will slowly drift southeastward the next few days. Trade winds will remain fresh with locally strong magnitudes through the windier channels and bays tonight. The high sliding southeastward will tighten the pressure gradient back across the islands enough to support sustained strong trades with gale gusts through the eastern island channels Sunday and Monday. Strong to near gale force trades will likely occur most of next week around Maui County, through the Alenuihaha Channel and over those waters south of the Big Island. There is a Small Craft Advisory (SCA) in effect through 6 AM HST Sunday for all of the Hawaiian coastal waters, with the exception of the Oahu and Maui leeward waters, due to strong trades and elevated seas. Strengthening trades will have this SCA expanding into the Oahu and Maui leeward waters from 6 AM HST onward Sunday. This all water SCA should remain in effect for the foreseeable future. North swells that have recently boosted north and west shore surf will slowly diminish tonight and level out Sunday. Northern and western exposures will experience well below advisory level surf the next couple of days as incoming overlapping north and northwest swells produce medium size surf. Surf along northern shores will become small from Tuesday onward as lingering north and northwest swells fade. The next moderate, low period northwest to north swells will arrive next weekend. Strengthening trades the first half of next week will build in an easterly swell and ultimately increase eastern-facing shoreline surf heights. There is a good chance that surf along Oahu and Kauai's eastern exposures will reach 8 foot surf advisory thresholds Sunday night or Monday morning and then build further statewide into Tuesday. Low, long period background southerly swells will continue to create small near seasonal surf along south-facing shores the next several days. && .HFO WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through late tonight for Kauai. Small Craft Advisory until 6 AM Sunday for all Hawaiian waters except Maui County Leeward waters and Oahu Leeward waters. Small Craft Advisory from 6 AM Sunday through 6 AM Monday for all Hawaiian waters. && $$ DISCUSSION...Birchard AVIATION...Burke MARINE...Blood Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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