| Current Conditions | ||
| Temp |  | 9.6 C |
| RH | | 32 % |
| Wind | | NE 11 mph |
| Road | | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 484 FXHW60 PHFO 182032 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 1032 AM HST Wed Sep 18 2019 .SYNOPSIS... Easterly trade winds will prevail over the next few days thanks to high pressure far north of the area. Clouds and passing light showers will tend to favor windward and mauka areas. Lighter winds along with a wetter weather pattern is expected beginning Friday and continuing through the weekend as a moist and unstable airmass moves in from the east. A more typical trade winds weather pattern is expected to return early next week. && .DISCUSSION... Surface high pressure is centered far to the north northeast of the area while an area of low pressure is centered several hundred miles to the west of Kauai. Radar and satellite imagery indicates that the low level wind flow across the area is slightly south of due east due to the lows proximity to the state. The airmass is rather stable across the area due to a ridge aloft. The 12Z soundings indicate inversion heights are around 6000 to 7000 feet. Light passing showers can be expected across some windward and mauka areas today but most locations will be generally dry. Some thin high clouds may also pass over the area from time to time due to deep convection west of the state. The surface high will drift slowly eastward over the next few days while the low to our west moves off to the northwest. The low level wind flow will become more easterly as the low pulls away from the area. Wind speeds will generally be in the light to moderate range. The ridge aloft will remain over the area through Thursday so shower activity will be highly dependent on incoming moisture availability and primarily fall over windward and mauka areas. A change to this weather pattern is expected as we head into the weekend. An upper low is forecast to move down over the area from the northeast while high pressure will remain far to the north northeast of the area. The upper low will destabilize the airmass across the area. In the meantime, moisture associated with a weak area of low pressure currently centered several hundred miles southeast of the state will move up over the area. Rainfall chances will increase beginning Friday over the east end of the state, then gradually spread westward over the weekend. The airmass may become unstable enough to allow for some thunderstorm development to occur especially during the afternoon and evening hours. Locally heavy rainfall is also a possibility across some areas. Winds will also become lighter due to lows proximity to the state. By Monday, the upper low is forecast to move off to the west of Kauai which will allow for a more stable airmass to move overhead. Trade winds are also expected to pick back up to moderate levels. Showers will then favor windward and mauka areas at that time. && .AVIATION... Moderate east-southeasterly winds continue across the island chain for today, but are expected to become more easterly to northeasterly by tomorrow. Scattered showers will impact mainly windward and mauka areas of the state throughout the day with leeward Big Island seeing an uptick in afternoon shower activity. Mainly VFR conditions are expected. No AIRMETs are currently in effect. && .MARINE... Fresh to locally strong, east to east-southeast winds will continue today due to high pressure to the northeast and a tropical disturbance moving northward to the west of the state. A shift back to a more typical east to northeast direction is expected Thursday through Friday. A Small Craft Advisory is now in effect for the typical windy areas around Maui and the Big Island through Thursday night. Guidance shows a return of light to moderate southeast flow late Saturday through Sunday due to an approaching trough from the east-southeast, which would support localized land and sea breeze conditions near the coasts. A series of small swells from the southwest and south are expected through the rest of this week. The largest of these looks to be towards the end of the week as a long-period south-southwest swell and short-period west-southwest swell combine across the area. This will likely boost surf along south and west facing shores late Thursday into Friday. A small northwest swell is possible late in the weekend into early next week. A small swell from Tropical Cyclone Kiko around Thursday along exposed east facing shores before dropping over the weekend. Surf heights are expected to be below advisory levels with all of these swells. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Friday for Pailolo Channel- Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Burke AVIATION...Dye MARINE...TS Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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