A rainy weekend is in store for the east and west coasts and the Hawaiian Islands.
Although rains heading toward the East Coast are not expected to cause widespread or significant flooding, it’s a different story for the Pacific Northwest and Hawaii where several inches of rain could cause flash flooding in mid urban, runoff from melting snow could cause streams and rivers to rise. and landslides constitute a real risk.
Severe thunderstorms hit the Gulf Coast Friday morning, bringing gusty winds, heavy rain and frequent lightning. During the day, thunderstorms will move east, bringing with them a risk of severe thunderstorms capable of causing damaging winds and a slight risk of tornadoes. Areas most at risk include southeastern Louisiana, southern Mississippi, southern Alabama and western Florida. Cities to watch include Mobile and Montgomery in Alabama and Pensacola, Florida.
Another round of rain will hit the Gulf Coast states again on Saturday. Through Sunday, 1 to 2 inches of rain could fall over this southern layer, with locally higher amounts reaching 5 inches.
Farther north, light rain is expected to move from the Midwest and Mid-Atlantic to the Northeast and New England by midday Friday. Precipitation should not be significant, but rather annoying. Even heavier rains are expected to hit these areas on Sunday.
Both sets of rain for the Mid-Atlantic, Northeast and New England will generally amount to 1 inch of rain or less.
While the East Coast will experience mostly light to moderate rain through the weekend, two storms are expected to affect the Pacific Northwest through the weekend and early next week.
A Flood Watch was issued Friday morning for much of Washington and Oregon and will remain in effect through Tuesday. This long-term flood watch was launched ahead of two atmospheric river-fueled storms expected to bring wind, rain and mountain snow to Washington, Oregon, Idaho and the North from California.
Rainfall of 3 to 7 inches will be possible, with the highest precipitation totals likely over the Cascades, Cascade Foothills and western Columbia River Gorge.
Several feet of snow are also expected in parts of the Cascades. Snow levels are initially expected to be high, with the greatest amounts of snow confined to the highest elevations. For this reason, the western slopes of the Cascades may be at increased risk of flooding due to increased snowmelt.
The active pattern for the Pacific Northwest will persist into next week, with another round of significant precipitation expected Monday through Monday evening, with the highest rain totals as over the Olympic Peninsula. As soils become more saturated with each successive storm, the threat of flooding will increase over time.
Outside of the continental United States, Hawaii is also facing a “Kona storm” that has already dropped rainfall totals into double digits on parts of the islands, with more expected on Saturday. All islands were under flood watch Friday morning.
An area of low pressure over the Pacific Ocean, known as the Kona Depression for this part of the world, fed large amounts of tropical moisture to the island chain, leading to torrential rains.
A Kona depression is described by the National Weather Service as a hybrid system between a winter storm and a tropical cyclone and is more common during the winter season. Kona’s lows are known to produce torrential rains, heavy mountain snowfalls, and severe thunderstorms capable of causing destructive wind gusts.
The heaviest winds will fall on the southwest slopes of the mountains, which are generally on the leeward (or “Kona” side) of the typical northeast trade winds. These are the locations where personal weather stations reported 15 to 17 inches of rain in less than 10 hours on Thursday.
More than 90 percent of Hawaii is in some sort of drought, but too much, too quickly brings the risk of flash flooding. Landslides were reported on Thursday, and the risk will continue through Saturday.
As the Kona Low recedes, a drier situation will prevail on Sunday.