| Current Conditions | ||
| Temp |  | 2.2 C |
| RH | | 69 % |
| Wind | | E 11 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 625 FXHW60 PHFO 220634 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 834 PM HST Sat Jul 21 2018 .SYNOPSIS... A high pressure ridge far to the north of the Hawaiian Islands will continue to keep the state in a moderate trade wind weather pattern through next week with clouds and showers favoring the windward and mountain slopes of each island. A few weak disturbances developing in the deep tropics will bring higher moisture amounts northward with periods of enhanced showers affecting the islands through week. The first round of enhanced showers will begin on Sunday and last through Tuesday morning. && .DISCUSSION... Two 1032 MB surface high pressure centers are far north of the islands this evening, one in the Central Pacific and the second high in the East Pacific, are helping to maintain a high pressure ridge north of the Hawaiian Islands through the week. A cold front moving south near the International Date Line will break down the ridge northwest of the islands as the East Pacific high builds. The break in this ridge will cause a slight shift in ridge axis, causing the trade wind directions to shift slightly towards the east with potentially a slight southeasterly component from Thursday through Friday, yet it will not significantly affect the moderate trade wind speeds. Three periods of wet weather are forecast through the week as several weak disturbances developing in the deep tropics will send plumes of higher moisture amounts northward with several days of enhanced showers across the state through the next seven days. The first round of enhanced showers will arrive on Sunday with higher low level moisture amounts producing increasing shower trends across all islands through the day. Precipitable Water (PW) amounts will range from 1.5 to 2.0 inches as this bands passes slowly through the state over the next few days. This evenings satellite imagery shows the leading edge of this deeper moisture plume is moving westward roughly 200 miles east of Hilo. Numerous showers will develop across Windward and Mauka areas with periods of showers drifting over leeward sections as the deeper moisture moves slowly through the state. More stable air will move into the islands decreasing shower activity a bit on Tuesday and Wednesday, with a brief period of higher trade wind speeds. A second elevated moisture plume will drift across the state on Thursday with PW amounts increasing back into the 1.5 to 2.0 inch range causing numerous showers along windward and mountain slopes with scattered showers over leeward areas from Thursday through Friday with a similar flavor of wet trade wind weather forecast for each island. More stable air moves back into Hawaii from the east from late Friday into Saturday. Longer range models hint at a third round of unstable moisture and showers reaching the Big Island by Saturday afternoon and spreading westward across the state through next Sunday. We will continue to monitor these periods of wet trade wind weather through the week. Stay tuned for updates as the weather pattern slowly evolves over time. && .AVIATION... Locally breezy east winds will persist through the coming week. Cloud and shower coverage will be relatively sparse through Sunday morning. VFR conditions will prevail. There will be isolated MVFR ceilings and visibility over east sections of the islands, but we do not anticipate that AIRMET SIERRA will be required for MTN OBSC. Clouds and showers will increase starting Sunday afternoon as low level moisture spreads over the islands from the east and MTN OBSC may become widespread enough to require AIRMETs. && .MARINE... Surface high pressure far north of the islands will continue to produce locally breezy trade winds into early next week. A Small Craft Advisory (SCA) remains in effect for Maalaea Bay and the Pailolo and Alenuihaha Channels through Sunday night. The SCA will likely continue for these waters, and be expanded to include the waters south of the Big Island, starting Monday due to a slight increase in trade wind speeds. A new long-period south swell will continue to fill in through early Sunday morning. This swell is expected to peak on Sunday, and then gradually lower from Sunday night through early next week. A High Surf Advisory remains in effect through Monday afternoon for south facing shores of all islands. Otherwise, only small background south swells are expected from mid-week into next weekend. The trade winds will continue to produce moderate short-period choppy surf along east facing shores through most of next week. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 PM HST Monday for Niihau-Kauai Windward-Kauai Leeward-Oahu South Shore-Waianae Coast-Molokai- Lanai Makai-Kahoolawe-Maui Leeward West-Maui Central Valley- Leeward Haleakala-Kona-South Big Island-Big Island North and East-Kohala. Small Craft Advisory until 6 AM HST Monday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel. && $$ DISCUSSION...Bohlin AVIATION...Powell MARINE...Houston Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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