Flash Flood Watch

...FLASH FLOOD WATCH FOR OAHU MAUI COUNTY AND THE BIG ISLAND... ...FLASH FLOOD WATCH REMAINS IN EFFECT THROUGH TUESDAY AFTERNOON... The Flash Flood Watch continues for * Kahoolawe, Lanai, Maui, Molokai, Oahu and the Big Island. * Through Tuesday afternoon

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4-6+ foot
Flat
0-2 foot
0-2 foot

Light winds continue across the coastal waters tonight. The background flow is expected to become more south and southwest overnight and Monday is response to a front moving towards the islands from the northwest.

The front will move towards the islands overnight and Monday, and reach Kauai waters by Monday evening. As it continues to move down the island chain, look for the front to reach Big Island waters Tuesday. Heavy showers and thunderstorms will be possible along and east of the front. Some of the thunderstorms may be strong enough to warrant Special Marine Warnings.

Behind the front, fresh to locally strong northerly winds are expected, but should become light to moderate northerlies by Wednesday, and persist through the remainder of the week.

The current northwest swell is expected to peak tonight along north facing shores just below advisory levels and then diminish Monday. A bigger northwest swell on Tuesday and Wednesday will likely produce surf well above the advisory threshold for north and west facing shores. The swell will also boost combined seas above the 10 foot level, so a Small Craft Advisory will likely be needed for exposed waters. An even larger northwest swell is forecast to arrive Friday. That swell could produce warning level surf along north and west facing shores.

A low east of New Zealand generated a swell which will produce surf near the advisory level along south facing shores through Monday.

Hawaii Wave Height Model

Tide Predictions

High tide at Kahului was 2.4 foot at 2:00 PM early this afternoon, dropping to a low of 1.0 foot at 2:00 PM early this afternoon, then rising to a high of 1.5 foot at 2:00 PM early this afternoon, before once again dropping to a low of 0.2 foot at 2:00 PM early this afternoon

The sunrise was at 06:23 am this morning and will set at 05:56 pm this evening. The Moon is currently 3 days old, and is in a Waxing Crescent phase. The next First Quarter will occur at 10:23 PM on Friday, October 27th.

Hawaii Wind Report

Maui Weather

70°/°
Wind: ESE at 8 mph
Sunrise: 6:24 AM
Sunset: 5:55 PM
current observations as of 6am October 23rd, 2017

Weather Outlook for Monday, 23rd October 2017

Summary

Heavy showers and thunderstorms associated with a strong cold front that is forecast to move down the island chain could lead to flash flooding, mainly from Oahu to the Big Island Monday through Tuesday. The front will reach Kauai late Monday with cool and dry air following as it moves down the island chain. The front is expected to pass east of the Big Island Wednesday night with dry northeast flow forecast for the second half of the week.

Detailed Discussion

Animated water vapor imagery showed an amplifying upper pattern across the northern Pacific that was characterized with a building ridge east of Japan and a shortwave trough digging southeastward toward the Hawaiian Islands. The latest surface analysis showed a cold front associated with the upper trough extending southwest to near Midway from a gale-force low centered around 1500 miles north- northeast of the state. A ridge axis was analyzed extending west- southwest within a couple of hundred miles north of the islands from 1030 mb high pressure centered over the far eastern Pacific. An ASCAT pass earlier today showed more of a weak east-southeast (5 to 15 kt) wind flow over the island chain due to the vicinity of the ridge axis. The evening radar loop showed much of the heavy showers and storms that developed earlier over the Hilo and Puna districts trending down and now focusing over the southeast Big Island coast across the Kau district.

For the overnight hours tonight through Monday, the threat for heavy rain will steadily increase across the island chain as deep tropical moisture continues to be drawn up from the south-southeast and the aforementioned cold front and upper trough approach. The latest satellite-derived precipitable water (PW) imagery showed a large area of 1.6 to 2+” values filling in over the Big Island and south of the islands. High-resolution model reflectivities support heavy showers developing within a pre-frontal convergence band early Monday morning in the vicinity of Oahu and the surrounding waters.

The latest near-term (Monday-Tuesday) guidance remains in good agreement and shows the cold front reaching Kauai Monday evening, Oahu late Monday night, then continuing eastward over Maui County and the Big Island Tuesday through Tuesday night. A combination of falling upper heights associated with the upper trough, increasing instability and isentropic lift, shear (effective 0-6 km bulk shear up to 40 kt), and plenty of deep tropical moisture will support heavy rain and thunderstorms through this period.

Impacts associated with this front and upper trough will include: the potential for flash flooding, strong thunderstorms (an isolated severe storm can’t be ruled out), gusty downslope winds mixing down over windward areas (Oahu and Kauai) where breezy southwest low- level flow is anticipated, and the potential for a wintry mix over the summits Monday night into Tuesday.

A flash flood watch remains in effect for Oahu, Maui County and the Big Island for the Monday through Tuesday period. A high wind watch remains in place for the summits on the Big Island for late Monday through Tuesday as southwest winds ahead of the upper trough strengthen and become hazardous (gusts to 65 mph).

Drier and cooler air with north-northeast flow will fill in across the islands through the second half of the week as the band of deep tropical moisture associated with the front exits to the east of the Big Island. Dewpoints are forecast to reach the 50s over Oahu and Kauai Tuesday through midweek in the wake of the front, then steadily climb back into the 60s through the second half of the week. Winds are forecast to weaken once again over the upcoming weekend as another, slightly weaker, cold front approaches the state.

Central Valley (Kahului, Spreckelsville):

FLASH FLOOD WATCH IN EFFECT FROM MONDAY MORNING THROUGH TUESDAY AFTERNOON. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Haze through the night. Lows around 68. Light winds. Chance of rain 30 percent.

Leeward West (Lahaina, Ka`anapali):

FLASH FLOOD WATCH IN EFFECT FROM MONDAY MORNING THROUGH TUESDAY AFTERNOON. Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Haze. Lows 67 to 74. Light winds. Chance of rain 40 percent.

Windward West (Wailuku, Waiehu):

FLASH FLOOD WATCH IN EFFECT FROM MONDAY MORNING THROUGH TUESDAY AFTERNOON. Mostly cloudy with scattered showers. Haze. Lows 60 to 73. Light winds. Chance of rain 50 percent.

Windard Haleakala (Hana, Haiku, Makawao):

FLASH FLOOD WATCH IN EFFECT FROM MONDAY MORNING THROUGH TUESDAY AFTERNOON. Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Haze. Lows around 70 at the shore to around 53 at 5000 feet. Light winds. Chance of rain 50 percent.

Leeward Haleakala (Kihei, Wailea, Makena):

FLASH FLOOD WATCH IN EFFECT FROM MONDAY MORNING THROUGH TUESDAY AFTERNOON. Mostly cloudy with scattered showers. Haze. Lows around 69 at the shore to 53 to 59 upcountry. Light winds. Chance of rain 40 percent.

Haleakala Summit

FLASH FLOOD WATCH IN EFFECT FROM MONDAY MORNING THROUGH TUESDAY AFTERNOON. Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 47 at the visitor center to around 44 at the summit. Southwest winds around 10 mph. Chance of rain 30 percent.

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