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Hawaii Island Weather Update for April 28th, 2019


Highway 250 in the area of the 16-mile marker is closed to all traffic due to flooding and heavy ponding on the roadway. Detour through Kohala Ranch. Use alternate routes of Kawaihae Road and Akoni Pule Highway for travel. Heavy to Moderate rain happening in the upper elevations and slowly moving makai.

Synopsis

A low pressure system and stalled cold front north of the Hawaiian Islands will bring continued light winds to the region. Expect enhanced showers with locally heavy rain and a few afternoon and evening thunderstorms through tomorrow as an upper level trough passes through the islands. The low drifts eastward on Tuesday and another surface high builds in from the west heralding a return to a drier trade wind weather pattern with windward and mauka showers through Thursday. Friday through next Sunday's weather pattern appears wet and unstable.


Discussion

Clouds and showers continue to build up over mountains and island interior sections this afternoon. A few areas showed rises in stream levels due to slow moving shower bands with heavy rainfall upstream leading to rapid runoff within the stream basins. These elevated showers will continue to develop through the overnight and Monday time periods as an upper level short wave trough moves from west to east across the state. There remains a chance for isolated thunderstorms over the next 24 hours as upper level forcing from this trough increases over each island.


In the big picture, a low pressure system with a stalled cold front lingers north of the Hawaiian Islands keeping a light and variable wind pattern in place across the state. Land and sea breezes will develop over each island for the next 24 hours. A combination of cooler air aloft and upper level forcing will keep unstable, humid and wet weather conditions around through Monday afternoon.


On Tuesday, Trade Winds are coming, with cooler drier weather returning to the island chain as the low drifts eastward and a high pressure system builds in from the west. Scattered showers will trend towards windward and mountain areas with drier conditions forecast over leeward areas. Moderate trade winds will last through Thursday.


On Friday, long range weather models continue to show another cold trough drifting into the Hawaii region. The cold air within this trough becomes cut off from the mid-latitude flow and forms an unstable upper low over the state. Weather impacts will depend on the track of this low and where it lands relative to the islands. However, the cold air aloft and upper level forcing associated with this system will probably produce another round of enhanced showers, locally heavy at times, and the potential for thunderstorms across the Hawaiian Islands through next Sunday. The forecast details this far out will likely evolve over time, so stay tuned for changes as the time period gets closer.

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