Koppu to Flood Philippines; Champi Not a Major Threat

Tropical storms Koppu and Champi are both expected to strengthen into typhoons over the next 24-48 hours. While Champi should not bring major impacts, Koppu is expected to lead to major flooding in the northern Philippines.

Tropical Storm Koppu is located about 995 km (615 miles) to the east of Manila, Philippines. Movement is to the west at 30 kph (18 mph). Maximum sustained winds are 95 kph (60 mph) with gusts to 120 kph (75 mph).

Tropical Storm Champi is located about 590 km (365 miles) to the east of Saipan. Movement is to the west-northwest at 28 kph (17 mph). Maximum sustained winds are 95 kph (60 mph) with gusts to 120 kph (75 mph).

Overall, we do not have any significant changes in the forecast for Koppu as it is still expected to slam the northern Philippines with very heavy rain and damaging wind through the weekend and early next week.

A continued track to the west is expected through the rest of the week which will put the storm to the east of Luzon Island in the Philippines by Friday and Saturday. During this time we should see Koppu strengthen and it should become a significant typhoon with wind as strong as a Category 3 hurricane by Saturday.

Impacts will begin across northeastern Luzon on Friday as rain starts, but significant impacts should begin on Saturday as rain and wind become more widespread. Flooding rainfall is expected to be the most significant threat across northern Luzon with wind damage the most likely along the east coast with gusts exceeding 100 mph near the center of the storm. Inland, wind damage should become more isolated.

From Saturday through Tuesday we expect to see bands of heavy rain move across northern Luzon, bringing 300-600 mm (12-24 inches) of rain to many areas. It is possible that some locations receive upwards of 900 mm (36 inches) of rain. While some rain will make it into Manila, flooding should not be a major threat as the heaviest of the rain remains to the north. To accompany flooding, mudslides in the mountainous terrain will be a significant threat as well.

Koppu will finally, slowly, begin to move to the north on Tuesday into Wednesday with impacts gradually winding down in the Philippines. Next in line for impacts will be Taiwan next week. While we will see bands of rain move into eastern Taiwan over the weekend, significant rainfall will hold off until closer to the middle of the week. At this time, there is still considerable uncertainty with the track of the storm this far in the future, but it does look like, at least, locally heavy rain will fall in Taiwan. The greatest threat for heavy rain will occur in eastern parts of the island. Depending on the track of the storm, we might have to watch for wind damage in southern Taiwan. Note that on the image above, impacts are only taken out to the 21st. It is likely that there will be additional impacts after the 21st, but confidence becomes lower.

It is also possible that during the middle of the week rain moves into southeastern China, but the amount of impact in this area is unclear due to low confidence in the track.

After this, there is even more spread in model solutions, but if the storm continues to the north into the East China Sea it will encounter increased wind shear and should significantly weaken. Because of this, if there are impacts to Japan, we still do not think they will be significant.

Tropical Storm Champi is the lesser concern of the two tropical storms in the western Pacific. We still think that Champi will gradually strengthen, probably becoming a typhoon while near the Marianas. Saipan is probably the largest island that will be impacted by this system as it will pass well to the north of Guam. Due to the relatively low population, impacts should be fairly minor. After this, a turn to the northeast is expected but the storm should not pose a threat to other significant land masses.

On the outlook we have added a low chance for development well to the east of the Mariana Islands next week. If this area does manage to develop into a tropical system, it is expected to move to the north into an area of high wind shear which should weaken it. Due to this, it should not be a threat regardless of development.

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