Jim Andrews

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Prapiroon Still Posing Forecast Puzzle

October 9, 2012; 8:53 AM ET

Typhoon Prapiroon may not have "tipped its hand" quite yet, as it's the range of possible outcomes for the storm has remained broad as of Tuesday.

What has seemed most clear is that Prapiroon will be slow to move for at least another two days or so, owing to weak steering winds.

However, slow movement would imply potential "indecision," being that minor, as-yet unclear factors will hold the key to storm behavior late in the week.

For one, the jet stream will track mostly west to east over China, Korea and Japan, well north of Prapiroon's location on Tuesday. Any buckling, however slight, could be enough to either "pick up" or suppress southward the typhoon later in the week.

Further, dry, stable air will continue to flow southward off the coast of east and south China, thereby setting up an unfavorable environment for a tropical cyclone. When presented with such an impediment, a vigorous cyclone can sometimes steer clear, tracking instead into alternate areas, having a more supportive atmospheric environment.

Still, the lack of a northward tug could allow the typhoon to continue towards the west and northwest, into relatively dry, cool air, perhaps ending up near Taiwan.

As for now, the path to a more favorable environment by Prapiroon would be one towards the north and east, tracking south of Japan. A buckling of the jet stream in the area of Korea could be enough to cause "recurvature" of the typhoon south of Japan late this week into early next week.

Although the above scenario is presented by widely available numerical forecast models as of Tuesday, these forecast tools showed rather ambiguous results on Monday.

Assuming that Prapiroon does indeed veer to the north and east before meeting is fate as a post-tropical storm over the cold northern Pacific Ocean, it would have the potential for adverse impact in mainland Japan.

Whether such impact be unpleasant rain, wind and wave, or a bout of heavy rain and high wind, will hinge upon how far north the typhoon swings before exiting to the east.

At the time of this infrared satellite shot (13:30 UTC Tuesday, Oct. 9, 2012), Typhoon Prapiroon had highest sustained winds of 80 mph, according to the Joint Typhoon Warning Center--JTWC. The center was pegged about 700 miles east-northeast of Manila, Philippines, and 600 miles south-southeast of Okinawa. Movement was towards the northwest at less than 5 mph. (Image: Japan Meteorological Agency--JMA)

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