Sunday, September 16, 2012

Hurricane Season Running Above Normal; Atlantic Not Obeying El Nino

The 2012 Atlantic Hurricane Season is entering its second half, and already we are above normal for total named storms.

The average number of named storms averages out to roughly 11 storms, encompassing tropical storms, hurricanes, and major hurricanes. The number of hurricanes overall stands at 6, while annually, major hurricanes strike about 2 times. This year, statistics show that we have had 15 total storms and 14 named storms (there was one unnamed tropical depression). It is only September, and we have passed the 1966-2009 annual total storm count. The number of hurricanes we have had this year is also above normal, with 8 recorded hurricanes thus far. It has been proven to be an active season. But not many expected this. In a way, this could be the Renegade Hurricane Season of 2012. But what made this season so unexpected?

The hot topic of El Nino (excuse the pun) is to blame. In an El Nino, which is defined as the warming of waters in the Equatorial Pacific Ocean, atmospheric winds in the Atlantic turn unfavorable for tropical cyclone development. The lowest number of named storms in the Atlantic actually result from an El Nino. However, as was explained above, this year is not the case. This could very well be the result of the lack of recognition of the El Nino, as was explained in a previous post.

Because this season has been so odd, the confidence of a long range forecast on the rest of the hurricane season is drastically reduced. However, if I were to take an estimate on what may happen, I have a feeling that this unusual activity will continue. Areas of possible development in the Gulf of Mexico and Caribbean at the time of publishing (uncommon for September tropical development) points to this as well.


1 Hour Winter Q-and-A on September 22 at 12:00 PM CT

Keeping with last year, I will be doing an hour-long question-and-answer session on the upcoming winter next Saturday, September 22, at 12:00 PM CT.

This is your opportunity to ask any and all questions relating to the upcoming winter!


'More Of The Same' Pattern To Continue

One of the best methods of forecasting is to use the persistence method, where you forecast based on past days. For instance, if it were hot for 3 days, you might assume it will be hot again tomorrow. If it were rainy for a few hours and the skies looked dark still, you might think it will keep raining. That rule is being applied to the next couple of weeks.

Currently, there is a big ridge in the West, and a very active storm track in the East. Helping this to happen is a positive PNA and negative EPO pattern. Below are their forecasts for the next 15 days.

Both indices are forecasted by the NCEP (Agency who manages the GFS, NAM, etc.), and the ESRL/PSD (the agency that is more on the technical side of models and forecasting.

Both agencies have the EPO heading negative in association with the ridge forming over the West. Considering it will be a strong ridge, I think the NCEP is correct in its assumption of the PNA over the next 15 days. As you can see, the PNA is much more positive with the NCEP than the ESRL/PSD, and I believe this is the correct way to go, based on how strong the models are with ridging in the West and troughing in the East.

Now that we are heading into Fall, such strong storms should become more common. I do not dispute that this could easily happen again in winter, as there has been much more persistent ridging in the upper latitudes than last year. It will be quite interesting to see if this pattern can get established for the fall and possibly winter.