| Current Conditions | ||
| Temp |  | 6.8 C |
| RH | | 37 % |
| Wind | | NE 24 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 583 FXHW60 PHFO 211942 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 942 AM HST Fri Sep 21 2018 .SYNOPSIS... Moderate to breezy trade winds will build across the state today as a weak trough near Kauai lifts away. Clouds and showers will favor windward slopes of all islands. A few afternoon showers will flare up along leeward slopes of the Big Island and on Kauai, where deeper moisture and higher humidity will linger. Winds will shift out of the southeast and south on Sunday and Monday, bringing humid conditions and potentially wet weather across the western end of the state through the middle of next week. && .DISCUSSION... A brief return to typical late summer trade wind weather is underway. The weak surface trough that passed overhead during the past two days is lifting north, allowing a surface high far northeast of the state to exert greater influence. As a result, easterly trade winds are building in from the east this morning and will strengthen through the day. Rainfall has been modest this morning and confined to windward slopes as stable conditions build in from the east. As is typical for summer, clouds and a few showers will develop across windward slopes this afternoon, and with deeper moisture lingering near Kauai, we cannot rule out an isolated heavier shower on the Garden Isle. Humidity will remain somewhat elevated on Kauai, while the rest of the island chain sees a drop in humidity as dew points fall back to typical September levels of around 70 degrees F. Stable trade wind weather will persist tonight and Saturday. Expect typical late summer conditions for the equinox. Easterly trades will hold at moderate to locally breezy strength. Ridging aloft will produce stable conditions with an inversion around 4000 to 6000 ft, keeping modest rainfall confined largely to windward slopes. A humid southeast to south flow will develop on Sunday, with wet conditions possible for the western end of the state into the middle of next week. A broad slow-moving area of low pressure will strengthen several hundred miles northwest of Kauai on Saturday night and Sunday. Locally, winds will initially shift out of the southeast, then veer out of the south for the western half of the island chain by late Sunday. This will draw up a very humid air mass from the deep tropics. Dew points will to rise several degrees above normal into the mid 70s, creating very humid conditions across all islands. A convergence band with deep moisture will set up just west of the state and may bring enhanced rainfall to parts of the island chain. There is still some disagreement between the GFS and ECMWF on the position of this feature, with the GFS bringing the deep moisture as far east as Kauai by Sunday night. As a result, there will be a chance of enhanced rainfall with heavy showers over Kauai, and as far east as Oahu, through the middle of next week. That said, uncertainty remains elevated. Across the rest of the state, mid level ridging should remain dominant, allowing modest showers along southeast facing terrain and spotty afternoon showers elsewhere. && .AVIATION... A stable easterly trade wind flow will build in from the east today as a trough near Kauai lifts away. Isolated MVFR conditions will be confined to windward slopes of most islands, and VFR conditions will dominate over most areas. However, with deeper moisture lingering near Kauai, more extensive clouds and showers will be possible for the Garden Isle through the afternoon. As the trades strengthen and the inversion builds around 4000 to 5000 ft, low level turbulence will increase over and west of terrain today. If conditions warrant, AIRMET Tango may be needed. && .MARINE... High pressure northeast of the state will keep a moderate to locally strong trade wind flow in place through Saturday. As a result, a Small Craft Advisory (SCA) remains in place for the typically windy waters around Maui County and the Big Island. An area of low pressure is expected to develop several hundred miles northwest of Kauai over the weekend, allowing the winds to weaken below SCA levels and shift around to the southeast Sunday through early next week. Surf will remain below advisory levels along all shores through the middle of next week. The current south swell will slowly decline through Saturday. Rough, short-period surf will remain around the summer average along east facing shores through tonight, then decline over the weekend. The first northwest swell of the season could arrive late next week, possibly reaching advisory levels along north and west facing shores. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Wroe AVIATION...Wroe MARINE...TS Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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