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Hawaii Island Weather Update for August 5th, 2019

Flash Flood Watch for Hawaii Island and High Surf Advisory for the East Facing Shores of Hawaii Island remains in effect until late Monday evening (August 5th).

Moderate to heavy rains have been reported in the Waiki'i and Pu'uanahulu area.

The National Weather Service (NWS) has issued the following advisories for Hawaii Island:


An unstable airmass with tropical moisture will continue the threat for flooding over Maui and the Big Island through late tonight. FLASH FLOOD WATCH REMAINS IN EFFECT THROUGH LATE TONIGHT The Flash Flood Watch continues for * Maui and the Big Island. * Through late tonight * An unstable atmosphere, combined with plenty of moisture will produce periods of heavy showers through tonight over the eastern half of the state as Tropical Cyclone Flossie passes northeast of both islands. PRECAUTIONARY/PREPAREDNESS ACTIONS... A Flash Flood Watch means that conditions are favorable for flash flooding. Flash flooding is LIFE THREATENING. Do not cross fast flowing water in your vehicle or on foot. Monitor later forecasts and be prepared to take action if a Flash Flood Warning is issued. If you experience heavy rain or rising water, head to higher ground immediately.


HIGH SURF ADVISORY FOR EAST FACING SHORES OF KAUAI OAHU MOLOKAI MAUI AND THE BIG ISLAND Advisory-level surf will continue along east facing shores through Tuesday as short-period easterly swell from Tropical Cyclone Flossie moves through the Hawaiian waters. HIGH SURF ADVISORY NOW IN EFFECT UNTIL 6 PM HST TUESDAY * SURF...6 to 10 feet along east facing shores of the Big Island and Maui. 5 to 8 feet along east facing shores of Molokai Oahu and Kauai. * TIMING...Through Tuesday. * IMPACTS...Moderate...Expect strong breaking waves, and strong currents making swimming dangerous. PRECAUTIONARY/PREPAREDNESS ACTIONS... Heed all advice from ocean safety officials and exercise caution.


Road and Facility Closures as of August 5th at 4:45 pm:

- Hawaii Police Department (HPD) and Hawaii Department of Transportation (HDOT) reports all road are open at this time and any closure can come without notice. They ask all motorist to drive with caution on our roadways.

- Bayfront Parking lot off of Kamehameha Avenue is closed.


Utility Outages as August 5th at 4:45 pm:

- Hawaii Electric Light Company (HELCO), Hawaiian Telcom, Spectrum, Department of Water Supply (DWS) all report no outages at this time.


Hawai'i Weather Outlook (as of 3:42 pm Monday afternoon)


Isolated thunderstorms remain a possibility through Tuesday afternoon. Light winds, muggy conditions and showers will continue across the islands beyond midweek. Expect more showers during the afternoon hours, mainly over interior sections of the islands.


Flossie's low level center is about 100 miles northeast of Hilo this afternoon. Thunderstorms associated with the system remain sheared well to the east of the low level center. A northeast to southwest oriented line of towering cumulus is about 100 miles to the southeast of the Big Island, and this band may reach the Big Island later tonight. The Flash Flood Watch continues for the Big Island and Maui through tonight.

Thunderstorms popped over the interior of the Big Island this afternoon, and we have had some flare ups on Kauai throughout the day. The forecast continues to carry the chance for thunderstorms into tomorrow due to the unstable airmass overhead. An upper level low remains to the northwest of Kauai, with its associated upper level trough extending from the low to the remnants of Erick which continue to track away from the islands.

Plenty of moisture is making its way over the islands, with the satellite derived precipitable water (PW) reaching 1.9+ inches just to the east of the islands. The afternoon Lihue sounding report 1.7 inches of PW, and the Hilo sounding had 1.8, so both in line with the satellite derived values. These values are above normal for August, but are not surprising given the tropical cyclone activity near the islands recently.

Showers across the islands today have spread from east to west in a trade wind flow, with some additional leeward and interior showers due to some pockets of lighter winds. Expect a transition from this to a more typical light wind afternoon convective pattern tonight and tomorrow.

Dewpoints are expected to remain in the 70s through the week, making it feel warm and muggy across the state. Light to moderate winds today continue a trade wind flow, but expect the winds to weaken tonight and tomorrow, and continue to be on the light side over the islands into the second half of the week. As a result, it will remain uncomfortable with showers forming over the interior of the islands during the afternoon hours. Limited clearing is expected overnight.

Have made some modifications to the PoPs/Sky/Wx and Wind grids. Winds in the first 48 hours were lightened to better reflect the high resolution model handling of the light wind pattern. The PoPs and associated parameters were adjusted for tomorrow night into Thursday night to reflect a more convective pattern that matches the land/sea breeze wind pattern over the land while the background trade flow begins to become more established.

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