Weather TALK [forecasts, etc]

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https://www.washingtonpost.com/blogs...-a-category-4/

Tropical Storm Koppu could bring disastrous rain to Philippines as Category 4
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By Angela Fritz October 14


Tropical Storm Koppu, currently disorganized and weak in the northwest Pacific, is expected to explode in intensity over the next four days as it tracks toward the northern Philippines. Koppu could make landfall as a Category 4 typhoon in Luzon over the weekend and linger there for more than three days, with flooding storm surge and over three feet of rain.

About 600 miles southeast of Luzon in the far western Pacific Ocean, Tropical Storm Koppu was a modest cyclone on Tuesday in a somewhat unfavorable environment. The wind shear is high, which acts to tear cyclones apart, and the thunderstorm activity is disorganized. Wind speeds are a manageable 45 mph.

But that is about to change as Koppu tracks west toward the Philippines through very warm ocean waters and a favorable atmospheric environment to strengthen into a powerful typhoon. Periods of rapid intensification are possible as the storm approaches the Luzon. The Joint Typhoon Warning Center is predicting Koppu will be a monster Category 4 typhoon with winds over 140 mph as it makes landfall in northeast Luzon, though the intensity forecast remains notably uncertain.

The typhoon’s winds may prove to be just one of Luzon’s worries. Forecast models suggest the storm will linger over the northern Philippines for three and a half days from Saturday into Tuesday. If that turns into reality, it would mean days of *******ial rain with the amplification effects of mountainous terrain and flooding storm surge as onshore winds drive ocean water over land.


In this scenario, the GFS model is predicting up to 50 inches — four feet — of rain in northern Luzon. Deadly mudslides would be an unquestionable threat. A non-landfall scenario for Luzon could actually deliver the worst blow to the island, since the storm’s core wouldn’t be weakened by the tall mountains.


While the final track of the storm is still very uncertain, Koppu will likely continue to track west over the next few days before an eventual turn to the north. When that turn occurs will determine if the Philippines or Taiwan end up feeling the typhoon’s greatest impacts.


Angela Fritz is an atmospheric scientist and The Post's deputy weather editor.