Hilo

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs around 81 near the shore to 66 to 71 at 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 66 near the shore to around 52 at 4000 feet. Southeast winds up to 10 mph shifting to the southwest after midnight. Chance of rain 50 percent.

Sunday: Mostly sunny with scattered showers. Highs around 82 near the shore to 66 to 72 at 4000 feet. Southeast winds around 10 mph. Chance of rain 40 percent.

Kona

Today: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 83 near the shore to around 69 near 5000 feet. West winds up to 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 69 to 74 near the shore to around 54 near 5000 feet. North winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Sunday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 83 near the shore to around 68 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs around 80 near the shore to 70 to 76 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 65 near the shore to 50 to 62 near 3000 feet. Southeast winds up to 15 mph. Chance of rain 40 percent.

Sunday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 81 near the shore to 71 to 77 near 3000 feet. Light winds. Chance of rain 40 percent.

Kohala

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs around 80 near the shore to 70 to 76 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 65 near the shore to 50 to 62 near 3000 feet. Southeast winds up to 15 mph. Chance of rain 40 percent.

Sunday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 81 near the shore to 71 to 77 near 3000 feet. Light winds. Chance of rain 40 percent.

South Big Island

Today: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs around 82 near the shore to around 67 near 5000 feet. East winds 10 to 20 mph decreasing to up to 20 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Breezy. Isolated showers in the evening. Lows around 70 near the shore to around 53 near 5000 feet. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers. Highs around 83 near the shore to around 66 near 5000 feet. East winds around 10 mph. Chance of rain 20 percent.

Puna

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs around 81 near the shore to 66 to 71 at 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 66 near the shore to around 52 at 4000 feet. Southeast winds up to 10 mph shifting to the southwest after midnight. Chance of rain 50 percent.

Sunday: Mostly sunny with scattered showers. Highs around 82 near the shore to 66 to 72 at 4000 feet. Southeast winds around 10 mph. Chance of rain 40 percent.

Waikoloa

Today: Mostly sunny. Isolated showers in the afternoon. Highs around 84 near the shore to 66 to 72 above 4000 feet. Northeast winds up to 10 mph shifting to the northwest in the afternoon. Gusts up to 30 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 66 to 74 near the shore to 49 to 58 above 4000 feet. Light winds becoming southeast up to 10 mph after midnight. Chance of rain 20 percent.

Sunday: Mostly sunny. Isolated showers in the afternoon. Highs around 84 near the shore to 64 to 71 above 4000 feet. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds are expected to continue through this afternoon. Low clouds and showers carried by the trades are mainly affecting windward sections of the state early this morning, especially windward Maui and the Big Island. The winds will weaken and become southeasterly starting this evening as a front approaches from the northwest. This front is expected to reach Kauai Monday night, and then stall near Oahu on Tuesday. The front will likely bring an increase in rainfall, especially along windward and north facing slopes of the western islands. Expect breezy trade winds from Tuesday through the middle of next week.

Discussion

A 1028 mb surface high pressure system is centered near 35N 144W, or more than 1200 miles northeast of Hilo. The tight pressure gradient southwest of this feature is producing moderate to locally breezy trade winds across most of the island chain early this morning. Elsewhere, the leading edge of a band of broken to overcast low clouds with embedded showers associated with a front is about 875 miles west-northwest of Lihue. The leading edge of this cloud band is moving toward the east-southeast at about 10 mph.
An upper-level low is evident about 340 miles south-southeast of Honolulu. Precipitable water (PW) values have increased to around 1.44 inches near Hilo according to the sounding profile this morning. Localized instability aloft associated with the upper- level low combined with the increased low-level moisture has resulted in some enhancement to low cloud cover and showers near the windward sides of the Big Island and Maui. Mid-level ridging is dominating the weather over the smaller islands. In addition, the atmosphere is rather dry near the western islands. The PW at Lihue is less than one inch, so there are only a few light showers embedded within the stable stratocumulus clouds west of Maui County this morning.
The latest output from the forecast models continues to show the surface high far northeast of the state moving eastward this weekend. There may be a few brief showers over some windward and mauka sections, especially the windward Big Island and Maui, from this afternoon into this evening. Some showers are also possible along the upslope sections of the leeward Big Island this afternoon, but most leeward areas of the smaller islands should remain rather dry.
Both the GFS and ECMWF models indicate the cold front, which was mentioned above, will approach the islands later this weekend. At the same time, the surface high will have moved far east-northeast of the state. This will cause the low-level flow to weaken and shift out of the southeast from tonight through Sunday. These winds may bring some slight increase in moisture to the islands ahead of the front, but there does not appear to be a significant surge of moisture from the tropical regions to our south. The global models agree that the front will reach Kauai by Monday night, but they differ on how far this front will eventually push down across the western end of the island chain. The GFS model brings it down near Oahu, while the ECMWF model appears to show it stalling just northwest of Oahu. We are indicating there will be increased clouds and rainfall over the western end of the island chain early next week, especially over windward and north facing sections of Kauai and Oahu. Then depending on how strong the front is, and how far down the island chain it pushes, there may be increased rainfall over portions of Maui County. The models also suggest some rainfall may occur over leeward sections of Kauai and Oahu. Note that we do not currently anticipate widespread flooding due to heavy rainfall with the arrival of this front. That being said, the moisture along the front combined with unstable conditions due to an upper-level trough associated with the front may produce some localized heavy downpours Monday night and/or Tuesday on Kauai.
As the front stalls out and weakens, surface high pressure will build in northwest of the state. This will cause breezy northeasterly trade winds to develop across the islands on Tuesday. These strengthening trades may also be relatively wet, especially across the smaller islands if significant moisture associated with the front lingers. This breezy, and potentially wet, trade wind weather pattern will likely persist through the middle of next week based on the latest guidance.

Aviation

A few showers continue to pass over the islands this morning with the latest radar trends showing the most persistent returns over the central and eastern islands, while satellite data continues to show an area of low/mid clouds maneuvering around the islands. Expect the best chances for showers and lower cigs to linger over the eastern and central islands, as 12z sounding data suggests better low lvl moisture at PHTO, while drier and more stable continues were noted over PHLI. Otherwise, moderate to breezy easterly trade winds will continue across the islands through this evening as a ridge of high pressure remains centered north of the state. Trade winds will begin to diminish from west to east Saturday night into Sunday, as the ridge of high pressure north of the state begins to lift northeast. VFR conditions are expected at most locations, with MVFR cigs and vsby expected within showers.
AIRMET Tango for low level mechanical turbulence downstream of higher terrain continues across all islands through the afternoon. AIRMET Sierra continues for central and eastern portions of the state, especially windward Big Island for tempo mountain obscuration as moist trade wind flow continues.

Marine

Moderate to locally breezy trade winds will continue today, so the Small Craft Advisory (SCA) has been extended through this afternoon for the typically winder waters around Maui County and the Big Island. Winds are then forecast to weaken and veer southeast through the rest of the weekend as a front approaches from the northwest. The front is expected to reach Kauai Monday night then stall near the central islands Tuesday, bringing an increase in showers across the western windward waters. Strong northeast winds will fill in behind the front and another SCA will likely be needed for most coastal waters by Tuesday morning and lasting through most of next week.
The current northwest swell is peaking early this morning and will gradually subside today through Sunday. A larger northwest swell build late Sunday night, with surf ramping up Monday, likely reaching advisory levels by Monday night and Tuesday, before slowly subsiding through the rest of the week. As this swell moves down the island chain the direction will become more northerly, most likely sometime Tuesday. This swell and the strong winds next week will also boost seas across most coastal waters to SCA level starting late Monday night.
East facing shores will have small, choppy surf through today, then slowly trend down through the rest of the weekend. Rough surf will return along east shores early next week due to the combination of north-northwest swell wrap and increasing northeasterly winds. By the end of next week, east shore surf could trend near advisory levels. Surf along south facing shores will remain small into early next week. A small south swell is possible towards the middle of next week.

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