A Bipolar Tropical Season for the Western Pacific Basin

September 08, 2014

Earlier this year I blogged about how a jackrabbit start for the Northwest Pacific typhoon season doesn't necessarily signal a banner year for typhoon counts there. I hate to say I told you so...but at this point the typhoon season is definitely way below a banner year.

The current total count stands at 13, whereas the average count at this point should be 14-16. So, despite the very inactive August and to some extent May and June, the typhoon count is really only just a little below the average at this point in the season. But this is mainly because of the very active start and a very active July in which five named storms formed.

These storms were fairly significant-three of them in particular: Neoguri, Rammasun, and Halong. All three dipped to or below 935 mb and Halong dropped to 915 mb, making it the most intense storm thus far this year. And Rammasun was the most intense storm ever to make landfall in China. Since then, however, only one storm formed in August-a record low for the month since Japan Meteorological Agency  began keeping records in 1951.

But as I noted in my earlier blog, a favorable Madden-Julian Oscillation (MJO), coupled with other favorable conditions with respect to shear, sea surface temperatures, and pre-existing monsoon troughs, can rack up typhoon counts in a hurry in any month. Especially in September.

Given the seesaw nature of the season so far, given the fact that it has been a quiet August, given the fact that the MJO is(over) due for another appearance, and given the fact that September is climatologically the second most productive month anyway, it is not unlikely that there could be a large number of storms that form in the coming weeks, which would rebound the seasonal count back on the plus side of normal.

But, consider this...looking back on the last 63 complete seasons, from 1951 through 2013, at all the times when the typhoon count was 13 or less at the end of August, only one season-1993-ended up at or above average (which I will set at 27 named storms) at the end of the season!

That said, armed with the statistics of a 63 year historical record for leverage, it is safer to say than not that we will probably come in just below normal-so I could go out on a limb and say that the Northwestern Pacific will likely see 26 or fewer storms when all is said and done on December 31. But I won't because AIR is not in the business of seasonal forecasting.

Of course, total storm counts alone do not a season make, and anticipating intensity and storm tracks are other matters altogether, and more difficult ones at that. I will leave that for another blog post.

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