Hilo

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 66 to 74 near the shore to around 58 at 4000 feet. Southwest winds up to 10 mph. Chance of rain 50 percent.

Monday: Partly sunny. Isolated showers in the morning. Highs around 84 near the shore to around 70 at 4000 feet. South winds up to 10 mph shifting to the east in the afternoon. Gusts up to 30 mph. Chance of rain 20 percent.

Monday Night: Mostly cloudy. Lows 67 to 74 near the shore to around 59 at 4000 feet. South winds up to 10 mph.

Kona

Tonight: Partly cloudy with scattered showers. Lows 70 to 77 near the shore to around 58 near 5000 feet. Light winds. Gusts up to 30 mph. Chance of rain 40 percent.

Monday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 85 to 90 near the shore to around 72 near 5000 feet. Light winds. Chance of rain 30 percent.

Monday Night: Partly cloudy. Lows 70 to 76 near the shore to around 57 near 5000 feet. Light winds becoming northeast up to 10 mph after midnight.

Waimea

Tonight: Mostly cloudy. Breezy. Lows 66 to 75 near the shore to 60 to 67 near 3000 feet. East winds up to 25 mph with gusts to 45 mph.

Monday: Partly sunny. Breezy. Highs around 83 near the shore to 73 to 82 near 3000 feet. East winds up to 20 mph.

Monday Night: Mostly cloudy. Lows 67 to 75 near the shore to 61 to 69 near 3000 feet. East winds up to 15 mph.

Kohala

Tonight: Mostly cloudy. Breezy. Lows 66 to 75 near the shore to 60 to 67 near 3000 feet. East winds up to 25 mph with gusts to 45 mph.

Monday: Partly sunny. Breezy. Highs around 83 near the shore to 73 to 82 near 3000 feet. East winds up to 20 mph.

Monday Night: Mostly cloudy. Lows 67 to 75 near the shore to 61 to 69 near 3000 feet. East winds up to 15 mph.

South Big Island

Tonight: Partly cloudy. Windy. Isolated showers in the evening. Lows around 76 near the shore to around 61 near 5000 feet. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 20 percent.

Monday: Mostly sunny. Windy. Highs around 84 near the shore to around 71 near 5000 feet. East winds up to 30 mph.

Monday Night: Partly cloudy. Breezy. Lows around 76 near the shore to around 60 near 5000 feet. East winds up to 25 mph increasing to 10 to 25 mph after midnight. Gusts up to 45 mph.

Puna

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 66 to 74 near the shore to around 58 at 4000 feet. Southwest winds up to 10 mph. Chance of rain 50 percent.

Monday: Partly sunny. Isolated showers in the morning. Highs around 84 near the shore to around 70 at 4000 feet. South winds up to 10 mph shifting to the east in the afternoon. Gusts up to 30 mph. Chance of rain 20 percent.

Monday Night: Mostly cloudy. Lows 67 to 74 near the shore to around 59 at 4000 feet. South winds up to 10 mph.

Waikoloa

Tonight: Partly cloudy. Lows 72 to 77 near the shore to 55 to 62 above 4000 feet. East winds up to 15 mph. Gusts up to 50 mph decreasing to 40 mph after midnight.

Monday: Mostly sunny. Highs 85 to 92 near the shore to 69 to 76 above 4000 feet. Northeast winds up to 10 mph shifting to the northwest in the afternoon.

Monday Night: Partly cloudy. Lows 72 to 77 near the shore to 56 to 61 above 4000 feet. Light winds.

Detailed Forecast

Synopsis

Strong trades will diminish during the next 24 hours and turn southeasterly Monday night into Tuesday. Showers increase over and around Kauai during midweek.

Discussion

Regional satellite shows Hurricane Nolo advancing westward well south of the Hawaiian Islands. Veered SE mid-level flow is piling up clouds over the SE-facing slopes of the Big Island, but moisture quality is rapidly diminishing as drier air works into the area. Widespread light to moderate showers this morning have diminished in coverage and mixed upslope and will eventually clear out tonight. A band of showery low clouds aligned parallel to the trades is taking aim on Kauai this afternoon where some enhanced coverage of showers late this evening. However, veering mid-level winds will eventually steer this moisture northwestward and away from the island.
Winds are diminishing as the pressure gradient over the islands gradually eases. Select zones in Maui County and on the Big Island are still experiencing gusts in excess of 50 mph, so the HWW has been transitioned to a Wind Advisory that will run through tonight. For remaining zones, wind headlines have been allowed to expire.
Attention for mid-week focuses on rainfall potential over Kauai, particularly the south and southeast facing slopes. A band of moisture presently on the NE side of Nolo extends southeastward into the deep tropics per visible imagery. This band will be drawn over Kauai Tuesday through Friday. Elevated moisture initially moves over the island on Monday, but dry low-levels and lack of ascent preclude an increase in pops as this likely amounts to nothing more than increased cloud cover.
PWATs are then poised to rise from around 1″ tonight to 2+” by Monday night as rich low-level moisture characterized by dewpoints firmly in the low 70s becomes established over the island. Weak but deep cyclonic flow coupled with gentle ascent caused by moisture advection will support increased showers over and around Kauai on Tuesday. Model cross-sections indicate rapidly diminishing boundary layer stability by late Tuesday which, combined with enhanced SE flow around the eastern periphery of Nolo should maximize orographic assistance. Coverage and persistence of rain is subject to some uncertainty, but given the broad/weak ascent field and lack of low- level forcing mechanism, suspect this will likely manifest as an enhanced coverage of quick-moving showers from the south and southeast. Waves of moisture advection then maintain some degree of enhanced shower activity over Kauai through Friday, but peak forcing and moisture depth will be late Tuesday through Wednesday with diminishing coverage likely thereafter.
Worth noting that this moisture will lift over the remainder of state by Wednesday perhaps supporting some increase in showers, though taken at face value decreased SE winds in the shadow of the Big Island and Maui may set the stage for some afternoon convection over Oahu Wednesday through Friday, becoming more likely each day as the gradient continues its weakening trend.
Guidance indicates the first cold front of the season reaching the western islands early next week. Southward progress of such fronts are generally overestimated by the models this early in the season, but indications are that it could be rather strongly forced, so it may nonetheless work into the area bringing with it decreased dewpoints and a modest increase in showers.

Aviation

Gusty winds will continue into tonight but will decrease Monday as Hurricane Nolo moves further away. Showers have become more isolated on the Big Island with only isolated MVFR now expected into tonight. Elsewhere, windward and mountain areas can expect some isolated MVFR ceilings and visibility tonight in any isolated shower that develops overnight.
Multiple PIREPs of low-level wind shear have been received near Kahului Airport (PHOG). Gusty easterly flow interacting with nearby terrain may be contributing to the reported shear. Additional low-level wind shear remains possible tonight, with the threat expected to diminsh by Monday as winds ease.
AIRMET Tango remains in effect for moderate to isolated severe turbulence below 9,000 feet over and immediately downwind of island terrain.
AIRMET Tango also remains in effect for sustained surface winds of 30 kt or greater across Maui and the Big Island.

Marine

Strong to near gale force trade winds and large, rough seas will gradually diminish tonight and Monday as the center of Hurricane Nolo moves northwestward roughly 275 to 325 nm south and southwest of Kauai. During this time, high pressure far north of the state will erode, and as Nolo moves farther west, the pressure gradient over the islands between the ridge and Nolo will weaken and allow the trades to ease. As a result, the Gale Warning that was in place for all waters has been downgraded to a Small Craft Advisory (SCA). Monday night through Tuesday night, the official National Hurricane Center forecast calls for Nolo to move toward the north-northwest and remain over 200 nm west of Kauai. Expect moderate to locally strong winds to veer out of the east- southeast to southeast during this time, requiring a SCA for exposed waters near some islands. Winds will gradually ease and back more easterly Wednesday and Thursday as Nolo moves westward away from the islands.
The broad area of strong to near gale force trade winds north of Hurricane Nolo has generated large and rough seas across the region. This fetch of winds and east swell/seas is weakening from east to west, and seas at the PacIOOS Hilo buoy, which have been dropping rapidly since midnight, fell below 10 feet at midday. A similar steep decline is anticipated at the Pauwela buoy north of Maui this afternoon, followed by Oahu and Kauai overnight. As a result, the High Surf Advisory (HSA) for east-facing shores of Big Island and Maui County has been cancelled, and the HSA remains in place for Oahu and Kauai through tonight. East shore surf will slowly decline Monday through Wednesday, though small, medium- period swells from distant east Pacific hurricanes will maintain moderate surf during the remainder of the week.
A mix of long to medium period south-southwest swell and building short to medium period south swell from Hurricane Nolo will keep surf along south facing shores elevated during the next couple of days. The longer period swell alone would produce surf near seasonal average, but the hurricane swell may push heights to the HSA level Monday. Given uncertainty, we will have held off on issuing an advisory for now, even though we are forecasting HSA level surf Monday. As Nolo makes a turn toward the north- northwest, the likelihood of advisory level surf from the shifting southwest swell will increase late Monday and Tuesday, especially across Kauai and Oahu. By Wednesday, the swell will switch out of the west.
On north facing shores, a small medium period swell will maintain small surf through Monday, followed by a decline Tuesday. Some wrapping west swell from Hurricane Nolo is possible by Wednesday.

HFO Watches/Warnings/Advisories

Wind Advisory until 6 AM Monday for portions of Oahu, Molokai, Maui, and the Big Island.
High Surf Advisory until 6 AM HST Monday for Olomana, Kauai East, Kauai South, Koolau Windward.
Small Craft Advisory until 6 PM HST Monday for all Hawaiian waters except Maalaea Bay.

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Data Courtesy of NOAA.gov