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Hawaii County Weather Forecast for September 20, 2022


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Hilo

Today: Partly sunny with scattered showers. Highs 80 to 86 near the shore to 68 to 74 at 4000 feet. North winds around 10 mph shifting to the east in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with showers likely. Lows 67 to 74 near the shore to around 56 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday: Partly sunny. Showers likely in the morning, then scattered showers in the afternoon. Highs 81 to 87 near the shore to 69 to 75 at 4000 feet. Northeast winds around 10 mph. Chance of rain 70 percent.

Kona

Today: Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 83 to 88 near the shore to around 70 near 5000 feet. Light winds becoming west around 10 mph in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy in the evening then becoming mostly clear. Isolated showers. Lows 70 to 75 near the shore to around 57 near 5000 feet. Northeast winds around 10 mph shifting to the west after midnight. Chance of rain 20 percent.

ARTICLE CONTINUES BELOW AD
ARTICLE CONTINUES BELOW AD

Wednesday: Mostly sunny. Scattered showers in the afternoon. Highs 82 to 87 near the shore to around 70 near 5000 feet. Light winds. Chance of rain 40 percent.

Waimea

Today: Breezy. Partly sunny with scattered showers. Highs around 83 near the shore to 74 to 81 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Showers likely in the evening, then scattered showers after midnight. Lows around 69 near the shore to 57 to 64 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday: Partly sunny with scattered showers. Highs around 84 near the shore to 75 to 81 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Kohala

Today: Breezy. Partly sunny with scattered showers. Highs around 83 near the shore to 74 to 81 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

ARTICLE CONTINUES BELOW AD

Tonight: Mostly cloudy. Breezy. Showers likely in the evening, then scattered showers after midnight. Lows around 69 near the shore to 57 to 64 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday: Partly sunny with scattered showers. Highs around 84 near the shore to 75 to 81 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

South Big Island

Today: Breezy. Sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 86 near the shore to around 74 near 5000 feet. East winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows around 71 near the shore to around 54 near 5000 feet. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Wednesday: Sunny. Isolated showers in the afternoon. Highs around 86 near the shore to around 74 near 5000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Puna

ARTICLE CONTINUES BELOW AD

Today: Partly sunny with scattered showers. Highs 80 to 86 near the shore to 68 to 74 at 4000 feet. North winds around 10 mph shifting to the east in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with showers likely. Lows 67 to 74 near the shore to around 56 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday: Partly sunny. Showers likely in the morning, then scattered showers in the afternoon. Highs 81 to 87 near the shore to 69 to 75 at 4000 feet. Northeast winds around 10 mph. Chance of rain 70 percent.

Waikoloa

Today: Sunny and breezy. Highs 83 to 89 near the shore to 70 to 77 above 4000 feet. Northeast winds 10 to 20 mph shifting to the northwest in the afternoon.

Tonight: Partly cloudy. Isolated showers in the evening. Lows around 74 near the shore to 53 to 61 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Sunny. Highs 83 to 88 near the shore to 69 to 76 above 4000 feet. Northeast winds around 10 mph in the morning becoming light.

Synopsis

Locally breezy trade winds will continue today, delivering just a few windward showers. Winds will gradually weaken tonight and Wednesday, and remain light to locally moderate through the weekend. The lighter trades will bring passing showers to windward areas, although a few brief showers may pop up over leeward areas in the afternoons.

Discussion

A surface ridge well N of the islands is providing locally breezy trade winds this morning. Regional satellite imagery shows scattered mostly stable low clouds immediately upstream of the islands, with a slight increase in low cloud cover noted a couple hundred miles to the E. A mid- and upper-level ridge directly over the islands is supporting a strong subsidence inversion, with 12Z sounding data indicating that it is based near 8 kft.
Latest guidance continues to indicate that a deep-layer cutoff low will develop far NW of the islands on Wednesday and Thursday, then slide SW away from the islands Friday into the weekend. The surface low is expected to weaken the trade-wind-supporting ridge to the N of the islands, and push it southward. Generally speaking, trade winds will weaken and veer to the E-SE near Kauai, while remaining moderate and out of the E near the Big Island, starting as early as tonight/Wednesday. Thereafter, subtle day-to-day fluctuations in wind speed and direction are anticipated through Saturday, but these will have little impact on sensible weather. Guidance continues to indicate lighter winds Sunday and Monday as compared to previous runs, as a low and front passing N of the islands keeps the surface ridge weak and suppressed southward. After this low moves NE, trade winds are now expected to strengthen Tuesday and Wednesday as high pressure builds N of the islands.
The mid-level ridge will prevail through the short-term, with just some brief weakening on Friday as the large cutoff low passes to the distant NW. The trough aloft supporting the surface low and front passing N of the islands Sunday and Monday may weaken the ridge, but the island atmosphere is expected to remain stable through the forecast period. While today looks to be fairly dry, a modest increase in moisture upstream of the islands is expected to fuel an increase in windward showers by this evening, with passing showers favoring windward areas through the period. Winds may weaken to the point that afternoon leeward sea breezes will be able to drive cloud and shower formation over interior and leeward zones, potentially as early as Thursday, but this is a low confidence forecast, with any showers likely to be short-lived.

Aviation

A surface ridge far north of the state is expected to maintain moderate to locally breezy trade winds through this afternoon. Some weakening of trade wind seeds is possible starting this evening based on the latest forecast.
The atmosphere remains stable, and there has been some drier air advecting into the state since last evening. Scattered to locally broken low clouds and brief trade showers are moving into the windward facing slopes of some of the islands early this morning. This is producing localized MVFR conditions, but VFR conditions prevail across most of the island chain. Looking upstream of the state, there appear to be pockets of slightly higher moisture moving toward the islands. The arrival of these areas of higher humidity might produce localized increases in the coverage of low clouds and trade showers along some windward sections later today or tonight. However, the stable atmosphere will likely result in only brief periods of MVFR conditions over windward sections through this afternoon.
AIRMET Tango remains in effect for TEMPO moderate low-level mechanical turbulence leeward of the higher terrain on all islands. This AIRMET will likely be needed through this afternoon due to the stable atmosphere combined with the locally breezy low-level trade wind flow. No additional AIRMETS are anticipated through this afternoon.

Marine

A Small Craft Advisory remains in effect for the typically windier bays and channels around Maui County and Big Island through this afternoon. A developing low northwest of the islands will weaken the surface ridge north of the area during the second half of the week, weakening winds and veering them from a more southeasterly direction.
Small, short period south and southeast swells will continue to decline today. A moderate, long-period south swell will arrive later this afternoon and move through the islands through the end of the week. A small northwest swell will fill in today, then decline through Wednesday. Strengthened trade winds will support elevated wind wave surf along east-facing shores today, then lower during the second half of the week as trades diminish.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST this evening for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov



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