Hilo

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 80 to 86 near the shore to 64 to 74 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 64 to 70 near the shore to around 57 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Friday: Mostly sunny with isolated showers. Highs 80 to 86 near the shore to 66 to 74 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Kona

Today: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 83 to 89 near the shore to around 69 near 5000 feet. Southwest winds up to 10 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 70 to 75 near the shore to 47 to 54 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 83 to 89 near the shore to around 69 near 5000 feet. West winds up to 10 mph. Chance of rain 20 percent.

Waimea

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs around 80 near the shore to 68 to 79 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 63 to 71 near the shore to 54 to 61 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 80 near the shore to 69 to 79 near 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Kohala

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs around 80 near the shore to 68 to 79 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 63 to 71 near the shore to 54 to 61 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 80 near the shore to 69 to 79 near 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

South Big Island

Today: Mostly cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 85 near the shore to around 67 near 5000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Tonight: Mostly clear. Lows around 73 near the shore to around 51 near 5000 feet. Northeast winds up to 10 mph in the evening becoming light.

Friday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 85 near the shore to around 67 near 5000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Puna

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 80 to 86 near the shore to 64 to 74 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 64 to 70 near the shore to around 57 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Friday: Mostly sunny with isolated showers. Highs 80 to 86 near the shore to 66 to 74 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Waikoloa

Today: Mostly sunny. Isolated showers in the afternoon. Highs 83 to 88 near the shore to 65 to 72 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows 71 to 76 near the shore to 49 to 55 above 4000 feet. Southeast winds up to 15 mph.

Friday: Mostly sunny. Highs around 86 near the shore to 65 to 73 above 4000 feet. Northwest winds up to 10 mph.

Detailed Forecast

Synopsis

A front approaching the islands from the north will introduce moderate to locally breezy trade winds and increasing shower chances for the western end of the island chain today through Friday as it moves south and then dissipates near Maui County. Light background winds will return and become more southerly from Friday night through the weekend, allowing daytime sea breezes and overnight land breezes to prevail throughout this period. Broad circulation around a low pressure system north of the state could bring enhanced rainfall over portions of the islands early next week.

Discussion

Early this morning, the band of clouds and showers associated with a surface cold front north of the state has become more diffuse as it continues to slowly move south towards Kauai. Latest satellite imagery shows that overnight land breezes have largely diminished cloud cover over the islands and kept showers to a minimum, with little to no rainfall reported across the state since early evening.
The front will continue to slowly sag southward closer to Kauai throughout the day, gradually increasing shower chances and low cloud coverage across the western end of the state. Based on the latest guidance, some minor tweaks were made to the timing of the front's progression, but the overall forecast philosophy remains in tact. The front is expected to move further south down the island chain, reaching Oahu by tonight or early Friday morning. Behind this feature, moderate to locally breezy northeasterly trade winds will build across the western end of the state. The front will likely dissipate on Friday before it reaches the majority of Maui County and the Big Island. Therefore, the eastern end of the state will likely remain in a rather dry land/sea breeze pattern through Friday.
This weekend, another front will approach the state from the northwest. While the main Hawaiian Islands will remain ahead of this feature, winds will become lighter again as it approaches, and the light background flow will veer to become more southeasterly initially on Saturday, then southerly or southwesterly by Saturday night into Sunday. Regardless, the light flow will result in a return of afternoon sea breezes and nighttime land breezes from Friday night into Sunday, especially for the wind-sheltered smaller islands. The general southerly background flow may bring an uptick in showers over some south and southeast facing slopes.
Beyond the weekend, models show a large low pressure system far north of the islands moving southward. The broad circulation around this low could transport enhanced moisture from the tropics into the islands Monday through Tuesday, potentially bringing an increase in showers over the islands, including normally dry leeward areas. Models continue to suggest that the bulk of significant rainfall will remain to the north and west of the main Hawaiian Islands, though there will be potential for deeper tropical moisture to be drawn northward over the eastern end of the state. The potential for enhanced moisture, along with instability from an upper-level trough over the area and daytime heating, could result in afternoon deep convection over interior/leeward Big Island Monday and Tuesday afternoons. While specifics largely remain unknown at this time, details will become more clear over the next several days as the event approaches.

Aviation

Early morning soundings indicate that the island atmosphere is stable, with a strong low-level subsidence inversion based near 6 kft. A shallow cold front about 75 nm N of Kauai is marked by a increasingly diffuse band of showery and stable low clouds, while a surface high pressure cell is centered NNW of the islands. As the high moves E over the next 24 hours, it will push the gradually weakening front over the islands of Kauai and Oahu, bringing an increase in mainly windward showers. Little in the way of upper-level support is expected, so widespread showers are not expected. While trade winds are currently on the lighter side, the high will increase the low-level pressure gradient, leading to increasing trade winds that may become locally breezy by tonight.
There are currently no AIRMETS in effect. Increased shower coverage over windward Kauai may require AIRMET Sierra for tempo mountain obscuration by this afternoon/evening, potentially spreading to Oahu by tonight. AIRMET Tango may be required for low-level turbulence to the lee of the mountains on Kauai and Oahu as trade winds increase.

Marine

Trades will hold in the light to moderate range through Friday for most areas, which will allow localized afternoon sea breezes and overnight land breezes to form near the leeward coasts. The exception will be over the Kauai and Oahu waters tonight through Friday as the tail-end of a weakening front drifts southward into the area, bringing fresh to locally strong trades to the surrounding waters. This will be short-lived due to another front approaching from the northwest, which will lead to a return of light and variable winds by Saturday. Moderate to locally fresh southerly winds are expected Sunday into early next week as this front nears the islands from the northwest.
Surf along exposed north and west facing shores will steadily lower through Friday as a north-northwest swell eases and shifts out of the north. After peaking well above predicted, early morning observations at the offshore NDBC buoys to the northwest reflect this downward trend and are now in decent agreement with guidance (peak spectral energy down into the 12-14 sec bands). This energy extrapolated through the islands supports advisory level surf continuing through much of the day today. Guidance shows this trend continuing through the weekend, with heights dipping below the advisory levels by Friday. Seas should hover just below the Small Craft Advisory level today, then continue to lower Friday into the weekend. A fresh north-northwest swell is forecast to build Sunday night and Monday, with surf potentially nearing advisory levels late Monday through Tuesday for exposed north and west facing shores of the smaller islands.
Surf along south facing shores will hold above the October average into the weekend as a new long-period, south-southwest swell arrives and peaks today through Friday. Surf will ease through the weekend as this swell moves out. An upward trend is expected again early next week with overlapping long-period, south- southwest swells expected. The first one should slowly fill in Monday through Tuesday, with the second and larger one expected Wednesday through the second half of next week.
Surf along east facing shores will remain small today, then pick up tonight through Friday for Kauai and Oahu as a moderate, short-period northeast swell arrives. This will be a short-lived event with a quick drop off expected Saturday.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for north and west facing shores of Niihau, Kauai, Oahu, and Molokai, and north facing shores of Maui.

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Data Courtesy of NOAA.gov