| Current Conditions | ||
| Temp |  | 4.0 C |
| RH | | 10 % |
| Wind | | NE 14 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 904 FXHW60 PHFO 250639 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 839 PM HST Thu Sep 24 2020 .SYNOPSIS... Fairly typical trade wind weather is expected through Saturday, with showers favoring windward and mauka areas and a stray shower spilling leeward from time to time. The trades will become light Sunday through Monday, with a few showers continuing to affect windward areas and a shower or two developing over leeward areas during the afternoon hours each day. A land breeze and sea breeze pattern is expected to take hold Tuesday through late next week, with limited to coastal areas at night and during the morning, and interior locations during the afternoon and evening hours. && .DISCUSSION... Currently at the surface, a 1025 mb high is centered around 900 miles north-northeast of Honolulu, and is driving moderate to locally breezy trades across the island chain this evening. Meanwhile, Tropical Storm Lowell remains far to the east of the state, around 1700 miles east of Hilo, over the cooler east Pacific waters. Closer to home, infrared satellite imagery shows scattered to broken low clouds pushing into windward areas with the trades, with mostly clear skies in leeward areas, with the exception of leeward Big Island where some lingering daytime heating driven cloud cover remains. Radar imagery shows scattered showers moving into windward areas, as well as increasing trade showers upstream of the state. Leeward areas remain generally dry, although a few diminishing showers continue to hang on over leeward Big Island. Main short term concern revolves around trade wind trends and rain chances during the next few days. High pressure north of the islands will keep moderate to breezy trades in place through Friday. The trades will then ease over the weekend as the high north of the state slides into the far east Pacific and a trough of low pressure develops north of the islands. A further easing of the trades is expected next week, as the remnant low of tropical cyclone Lowell approaches from the east, and a cold front approaches from the west. This is expected to drop trades into the light range Monday through late next week, with a sea breeze/land breeze pattern likely in leeward areas each day. As for the day to day weather details, fairly typical trade wind conditions will prevail through Saturday. Showers will favor windward and mauka areas, particularly during the night and early morning hours, with a stray shower reaching leeward areas from time to time. Shower coverage is expected to be the greatest tonight, before becoming more sparse Friday into the weekend. The forecast becomes a bit more uncertain Sunday and Monday, as the ECMWF shows a band of moisture ahead of the remnants of Lowell pushing into the islands, while the GFS keeps this band of moisture northeast of the state. With the lightened wind regime anticipated, we should see showers limited to windward areas during the night and morning hours, with a few daytime heating and sea breeze driven showers possible in leeward areas. Tuesday through next Thursday, the trades will be largely cut off, and this should result in a fairly dry land breeze/sea breeze driven shower pattern. During this time, showers should favor coastal areas overnight and during the morning hours, and interior sections of the islands during the afternoon and evening. && .AVIATION... Locally breezy trades will remain relatively dry through the forecast period. Prevailing VFR is forecast with only isolated/brief instances of MVFR expected within heavier windward and mauka showers, especially Maui and Big Island. AIRMET Tango is in effect for tempo low-level turbulence over and south through west of the mountains of all islands. Conditions will likely continue well into Friday. && .MARINE... Fresh to strong easterly trades will continue through Friday, then gradually trend down over the weekend, potentially enough for a localized land and sea breeze pattern to set up near the coasts beginning as early as Sunday. The Small Craft Advisory currently in place through the night will likely need to be extended through the day Friday for the windier waters around Maui County and the Big Island. Guidance shows the light winds holding through the first half of next week in response to a weakness developing in the ridge as a series of fronts pass to the north. Surf along north facing shores peaked today due to the first sizable swell of the season arriving out of the north. The latest observations at the offshore buoys suggest this swell has peaked. Expect plenty of energy holding into Friday, before dropping off quickly through the weekend. The active pattern across the northern Pacific is forecast to continue over the weekend through early next week with back-to-back systems diving southeastward across the Date Line from the western Aleutians. If this scenario materializes, the first swell will arrive Wednesday and peak Thursday with the second one arriving Friday. The first of the two could approach the advisory level by Thursday. Surf along south facing shores will remain up over the weekend as a new, long-period south-southwest swell arrives Friday from recent activity down south. Heights will near the advisory level (8 ft faces) by Saturday as it peaks. A gradual downward trend is expected Sunday into early next week. For the long range, the active trend is expected to continue down south around New Zealand within Hawaii's swell window. The latest guidance depicts a broad, storm-force low bottoming out at 929 mb south-southeast of New Zealand late this weekend. A large area of gale- to storm-force winds setting up within our swell window will drive seas into the 35 to 40 ft range. If this evolves as predicted, expect a large south swell by the end of the first week in October. Surf along along east facing shores will remain small through the upcoming weekend. A small easterly swell from tropical cyclone Lowell in the eastern Pacific can't be ruled out early next week, especially for the eastern end of the state. Water levels will gradually trend down each day through the last week of the month and into October. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Friday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Jelsema AVIATION...JVC MARINE...Gibbs Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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