| Current Conditions | ||
| Temp |  | 5.0 C |
| RH | | 11 % |
| Wind | | NE 17 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 823 FXHW60 PHFO 161330 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 330 AM HST Mon Jul 16 2018 .SYNOPSIS... High pressure far to the north of the Hawaiian Islands will continue to produce moderate trade winds across the area through this week and into next weekend. Clouds and scattered showers will tend to favor windward and mauka areas with just isolated showers possible over some leeward locations. A trough passing south of the state on Wednesday will produce increased showers along windward slopes of the Big Island and Maui. Otherwise a drier trade wind pattern will prevail through Saturday. && .DISCUSSION... This mornings satellite imagery continues to show an active Tropical Upper Tropospheric Trough (or TUTT) roughly 800 miles northwest of the state with several upper lows embedded in the trough axis. High level cirrus clouds are drifting from west to east across the region due to divergent upper level westerly winds. Bands of more stable stratocumulus and closed cell cumulus clouds are drifting across the islands with the trade winds. In the big picture, a high pressure ridge remains in place far to the north of islands through this week and into next weekend. Expect a decrease in shower activity today and Tuesday as a building high pressure ridge aloft produces more subsidence and stability over the islands. The trade wind subsidence inversion will range from 5,000 to 7,000 feet over the next two days keeping scattered showers along windward and mountain slopes with only isolated showers possible over leeward areas. On Wednesday, a weak disturbance in the deep tropics passing south of the islands will push higher moisture amounts up into the eastern half of the state with enhanced windward showers forecast over the Big Island and Maui. Otherwise, a drier and more stable trade wind pattern will prevail with scattered showers forecast along windward and mountain slopes with isolated showers possible over leeward areas from Thursday through Saturday. Over the next three to seven days the deep tropics southeast of the islands will become more active with several disturbances developing in the long range model guidance. These troughs may bring periods of increased moisture amounts up into the island trade wind flow as they drift westward, resulting in periods of higher chances for rainfall mainly along windward slopes. These higher moisture amounts will reach the southeastern half of the state more easily and that means both Hawaii and Maui Counties will have a higher chances for enhanced shower activity starting on Sunday. This far out in the extended forecast period we have lower confidence in the arrival timing of these increasing shower trends. Stay tuned as this upcoming active long range trade wind weather forecast evolves over time. && .AVIATION... Moderate trade winds will persist through tonight. Low clouds and showers carried by the trade winds will remain concentrated over windward and mountain areas of the state. This will likely produce brief periods of MVFR conditions along windward sections. A few light showers may be carried over to leeward sections of some of the smaller islands this morning, but VFR conditions are expected to prevail there. AIRMET Sierra remains in effect for mountain obscuration on Kauai, Oahu, Molokai, Lanai, and Maui. This AIRMET may be continued for windward Kauai beyond 6 AM HST this morning, but conditions appear to be improving across the other islands. && .MARINE... High pressure north of the islands will continue to generate trade winds across the islands this week. Locally breezy trades has led to a Small Craft Advisory (SCA) for the typically windy waters around Maui County and waters south of the Big Island. This SCA is good through Tuesday afternoon. Additional extensions of the SCA are likely to follow. An area of low pressure associated with a low pressure system will be passing south of the islands at midweek, which may bump up the trades another notch or two as well the need to expand the coverage of the SCA. Trade winds will produce surf mainly in the moderate range along the east facing shores this week. The strengthening trades at midweek will bump up the surf to near advisory level for the east facing shores. The current south southwest swell will maintain small to moderate surf along the south and west facing shores. This swell will slowly fade through Monday night. A small to moderate south swell with a similar size is due in Wednesday night. An even longer period of 21 seconds and a 2 foot south swell, will arrive over the upcoming weekend, resulting near advisory level surf for the south facing shores. A slight chance of thunderstorms remains across the northern offshore waters through tonight due to the presence of an upper level trough. The low pressure area passing south of the islands may bring a slight chance of thunderstorms to the far southern offshore waters around mid week. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Tuesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Bohlin AVIATION...Houston MARINE...Lau Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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