| Current Conditions | ||
| Temp |  | 8.5 C |
| RH | | 40 % |
| Wind | | NE 22 mph |
| Road | | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 647 FXHW60 PHFO 170614 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 814 PM HST Mon Sep 16 2019 .SYNOPSIS... Moist and unstable conditions associated with an upper disturbance and surface trough of low pressure in the vicinity of the islands will keep the potential for locally heavy showers in the forecast overnight into Tuesday. A return of drier air and more stable conditions is anticipated from east to west Tuesday night through Thursday. Increasing moisture and rain chances will become a possibility once again over the upcoming weekend. && .DISCUSSION... Water vapor imagery showed a broad upper low centered a several hundred miles north-northwest of the islands with plenty of middle- to upper-level moisture pooling northeastward across the region to its southeast. Recent satellite-derived precipitable water (PW) imagery reflected this with pockets of higher moisture near or around two inches over the western end of the state, which is well above average. This upper feature combined with a tropical disturbance several hundred miles south-southwest of Kauai and plenty of deep tropical moisture continues to fuel spotty heavy showers this evening. Latest radar loop showed a plume of moderate to heavy showers developing downwind of Oahu over the Kauai Channel that was expanding in coverage toward Kauai. The short-term guidance (through Tuesday) remains in good agreement and depicts a similar pattern continuing, which will keep the potential for localized heavy showers in the forecast. The better instability and deep tropical moisture are forecast to hold over the western end of the state as the aforementioned tropical disturbance south-southwest of Kauai slowly lifts northwestward. Model PWs will hold around two inches over these areas (highest Kauai). Light to moderate low-level east-southeast flow will prevail, which could translate to localized sea breezes Tuesday afternoon. Conditions will gradually improve over the eastern end of the state, as more stable and drier air move in from the east. Guidance remains in decent agreement Tuesday night through the second half of the week and reflects a return of drier and more stable conditions. Consensus shows the bulk of the deep tropical moisture shifting west of the islands, closer to the tropical disturbance lifting northwestward. This will translate to decreasing rainfall coverage. East-southeast low-level flow will likely hold through midweek, depending on how this tropical feature evolves, before shifting back to a more typical easterly direction around Thursday. Despite some differences between the various model solutions, a return of light winds and increasing moisture (two inch PWs) will be possible Friday night into the upcoming weekend as a trough associated with a tropical disturbance to the south moves through. Added instability associated with an upper low setting up over the state combined with this moisture will support increasing rainfall chances. && .AVIATION... A high pressure center far north of the Hawaiian Islands will keep light to moderate trade winds in the forecast for the next 24 hours. Sea breezes will develop along the sheltered western slopes of each island with some variability in wind directions along most southwest sides of each island. Deeper moisture and instability will linger over Kauai on Tuesday with enhancements to both clouds and showers, with brief periods of MVFR conditions possible. Elsewhere expect drier conditions with more typical windward and mountain showers favoring the overnight and early morning time periods. AIRMET Zulu remains in effect for light icing 160-FL280. No other AIRMETs in effect. && .MARINE... Moderate to locally fresh east-southeast winds will hold through midweek as a tropical disturbance to the south-southwest lifts northwestward. A shift back out of a more typical east to northeast direction is expected Thursday through Friday. This transition will be short-lived, however, due to an approaching trough from the east-southeast. Guidance shows a return of light to moderate east-southeast flow late Saturday through the second half of the weekend, which would support localized land and sea breeze conditions near the coast. A series of small swells from the southwest, south, and southeast is expected this week. The largest of these swells looks to be towards the end of the week as a combination of a long-period south-southwest swell and potential short-period southwest swell moves in across the area. Surf heights are expected to be below advisory levels with these swells. Small surf is expected along north, east and west facing shores through the new week. Expect a small east swell from Tropical Cyclone Kiko as early as Wednesday along exposed east facing shores and likely continuing through the weekend. Exposed west shores may see some of the aforementioned southwest swell on Friday. A small northwest swell will be possible late in the weekend into early next week. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Gibbs AVIATION...Bohlin MARINE...Kino Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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