| Current Conditions | ||
| Temp |  | 2.4 C |
| RH | | 7 % |
| Wind | | NE 25 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 909 FXHW60 PHFO 210630 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 830 PM HST Sun Sep 20 2020 .SYNOPSIS... A ridge of high pressure north of the state will keep moderate trade winds in place through the week, with only minor fluctuations in strength. Fairly typical trade wind weather will persist, with showers favoring windward and mauka areas, particularly during the night and early morning hours, and a stray shower reaching leeward areas from time to time. && .DISCUSSION... Currently at the surface, a 1023 mb high is centered around 1100 miles northeast of Honolulu, while an elongated area of low pressure is located around 550 miles south-southeast of Hilo. The gradient between these features is producing moderate trade winds across the island chain this evening. Infrared satellite imagery shows a mix of low and high clouds producing partly cloudy conditions in most areas, with a few locales seeing a bit more cloud cover. Radar imagery shows isolated to scattered showers moving into windward areas. The shower coverage is highest over Kauai, where a few showers are drifting into leeward areas as well. Main short term focus revolves around rain chances and trade wind trends. A ridge of high pressure north of the islands and a fairly active Intertropical Convergence Zone (ITCZ) to the south of the state, will maintain fairly steady moderate trade winds through the week, with only minor fluctuations in strength. We could see the trades ease a bit next weekend however, as both the GFS and ECWMF are advertising a front making some progress southward towards the island chain. Day to day weather trends will be difficult to pin down with too much specificity given the lack of any real substantial moisture sources upstream of the state. Overall, expect a fairly typical or perhaps slightly drier than normal trade wind weather pattern to persist through the next week. This should result in a continuation of scattered windward/mauka showers, particularly during the night and early morning hours, with a stray shower reaching leeward communities from time to time. There could be a bit of an increase in shower coverage across portions of the island chain Wednesday and Thursday however, as some of the remnant moisture associated with the former east Pacific tropical cyclone Karina slides through. No significant rainfall is expected through the next 7 days. && .AVIATION... The high pressure ridge north of the islands will weaken over the next few days, producing moderate easterly trade winds across the region. Periods of showers will continue to fall across windward and mountain areas with isolated showers along leeward areas. Expect brief periods of MVFR conditions in SHRA mainly in the overnight to early morning hours along windward and mountain slopes. Tempo mountain obscurations are possible through the early morning hours mainly along north and east sections of Kauai and Oahu. No AIRMETs in effect. AIRMETs for Tempo Mountain Obscuration are possible later tonight through Monday morning. && .MARINE... Moderate to locally strong trades will hold through tonight, then weaken slightly to moderate speeds as the ridge far north of the islands weakens. A stronger area of high pressure will move into range north of the islands about Tuesday night to Wednesday time frame, leading to a boost in the trades to locally strong levels again. This new high will continue moving east through the rest of the week while maintaining locally strong trades. A Small Craft Advisory (SCA) remains in effect through late tonight for the typically windy areas around Maui County and waters south of the Big Island. Trades will then be near borderline advisory levels to about Tuesday night/Wednesday, followed by the locally strong trades for the rest of the week, at which point a new SCA is likely for the typically wind waters of Maui County and waters south of the Big Island. A north swell is running at around 2 feet this evening, pretty much in line with WAVEWATCH III. A new long period north-northwest swell is due in Tuesday night, peak Wednesday night and Thursday at around 6 feet and 15 seconds, followed by a gradual decline through Friday. This translates to surf just below advisory levels. The short period trade wind surf along east facing shores will remain small, even more so with the weakening trades in the next 24 hours. Surf along east facing shores will increase slightly during the second half of the week with the anticipated boost in the trades. The arrival of the long period north-northwest swell may add another foot resulting in moderate surf during the second half of the week. The current south-southwest swell has peaked, but a small southwest swell is due in Monday, leading to near summer time average of 3 to 5 feet during the first half of the week. Another small south-southwest swell is possible Friday into Saturday. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Monday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Jelsema AVIATION...Bohlin MARINE...H Lau Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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