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.

Andrew

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!

Andrew

'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.

Andrew

Tropical Corner: Invest 92 Eyeing Caribbean, Gulf of Mexico Path

Good evening everyone, and welcome to the new Tropical Corner, where we discuss tropical weather across the Atlantic and East Pacific. Tonight, we are checking out Invest 92, just to the east of the Caribbean.

Invest 92 currently has a 20% chance of development per the National Hurricane Center, thanks to unfavorable upper level winds. However, as Invest 92 progresses west into the Caribbean, model guidance is suggesting strengthening will occur.

UW-Milwaukee

Model guidance for Invest 92 has the system possibly achieving Category 3 hurricane status as it gets going into the Caribbean. The track forecast remains unclear, with some models taking the system north west, more towards the Gulf Coast. Others take it west and well into the Caribbean.

UW-Milwaukee

There appears to be a slight consensus of a west-northwest movement, but after that, it all breaks down as far as confidence goes.

This is a brief article, as I am strapped for time. I will revisit Invest 92 tomorrow with much more information. The Tropical Corner should be a regular segment, and I hope you will like it!

Andrew

Has A Strong Trough Hit The North US Before, and What Does It Mean For Fall?

Model forecasts are pointing towards a monster trough entering the North Central US in the next couple of weeks. This trough is forecast to sit and be pretty much stationary over the region for a bit. This is not something we see too often, so we look to see if it's happened before. So, have we seen this before?

This is a chart of September 22nd in 1983. It shows 500mb vorticity on the top left, with 1000-500mb thickness and high/low pressure markings in the top right. The bottom two boxes contain different relative humidity values. Specifically, the 700mb RH on the left and 850mb on the right.

As you can see, a very strong disturbance is stationed over the north central US, pulling in below-freezing air into the Midwest. This below-freezing air is shown as the 540 red dashed line dipped into the Midwest and Northern Plains. It looks like some snow may have fallen over parts of the region above the 540 line.

So, what does 1983 have anything to do with 2012?

Analogs can be pretty powerful. Taking a look a week or two past this date, and here is what I find in the atmosphere after this date:

•Disturbance moves towards the Southwest and rapidly strengthens.
•Heat re-surges into the Plains and Midwest.
•Progressive disturbances move thru the US/Canada border.
•Another strong disturbance brings below-freezing air into the north central US on October 13.

What can one draw from all of this?

If we are to look at the ENSO phase, we see a strong El Nino in early 1983 progressing into a La Nina in the late fall and winter months, so this won't exactly play out. But, should this strong disturbance that is forecast to hit the North Plains and Midwest verify, 1983 could hold some hints. I do not doubt that the heat resurges into the nation, but a more active jet stream is not out of the question.

Time will ultimately tell, but analogs can be one of the most powerful tools forecasters can use.

Andrew