August Hurricane Season Update 5 months ago

August 7, 2018

  • The final forecast has a lower number of storms and total Accumulated Cyclone Energy (ACE).
    • The area of highest activity is the same.
  • The forecasted Sea Level Pressure patterns feature similarities to the top-10 low Accumulated Cyclone Energy seasons.
    • Though, the very warm water in-close makes for challenges.

There is no change in the area of highest concern. We have seen Subtropical Storm Alberto and Hurricane Chris in that area. Indeed, a sub-tropical feature (Debbie) also formed today.

The pre-season suspicion of the shut down of the Main Development Region continues to evolve as we had foreseen. Pre-season discussions talked about this and now that the "meat" of the season is around the corner, the numbers have been lowered. It does not change the worry about features farther to the north.

The difference from this year to last year in Sea Surface Temperatures is stark. It is almost the exactly the opposite.

The Euro forecast, from May, was on top of this and was hostile. Recently, it has not backed down! In addition, its pressure forecast for August-October is more hostile than before and is as opposite as you can get to last year's:

This is very bearish for the Main Development Region. There still remains the concern that with very warm water temperatures relative to average off the Northeast Coast (even with near average Gulf of Mexico temperatures which are very warm anyway) that storms, which may not be strong in the Main Development Region, will cause problems there.

Sea Surface Temperature in-close are boiling:

The bottom line is that we are lowering the forecast expectations for the season as a whole. Let's remember that in March we started around normal and then predicted lower than average in May, while alluding to the idea it could go lower. Amazingly, it is following in the footsteps of the 2005-2006 tandem, though the Sea Surface Temperatures in 2006 were a bit warmer than what they are now. Therefore, it is likely to be a lower that average season. It is not the absolute value of the SSTs, but rather what kind of patterns that are set up as a result of the warming of the tropical Pacific and of the cooling of the Main Development Region. This promotes higher than normal pressure over the Main Development Region and the faster easterlies underneath which lead to increased wind shear. It's all linked and has all come together (or compared to last year, unraveled). In fact, we may see the complete opposite of what we saw last year where the Western Pacific leads the way relative to average Accumulated Cyclone Energy while the Atlantic is the place that is lowest relative to average.

From the May discussion:

This does not mean we dismiss this year as non-challenging! In 2002, Isidore and Lili set a record for two Category 4s in the Gulf of Mexico within 10 days. Isidore turned to the west-southwest into the Yucatan rather than the forecasted track (which as of the Saturday before had the storm turning to the west-northwest). If the track forecast had been right, a Category 3 or 4 would have been heading for the Texas Coast. The Yucatan hollowed the storm out and it never came back strongly, though it was a big enough feature that by the time Lili went through she fell apart from a Category 4 to a Category 1 at landfall (though it was called a Category 2). The pressure rose to over 30 mb in 12 hours. If both had carried out their potential, it would have been only second to the Katrina-Rita double team in 2005.

In 2006, Ernesto could not avoid land, and so it never cranked up, in spite of Labor Day wind gusts over 90 mph around the Tidewater, while it was in its nonclassified state.

In 2009, Bill was as a major hurricane off the East Coast. In 2014, we had Hurricane Arthur come on July 4th weekend. Note that Arthur was the strongest early hurricane on the North Carolina coast. The El Niño evolved later in the year, but it goes to show how the East Coast must stay on its toes. In 1991, Hurricane Bob was an El Niño year and beat out Hurricane Carol's wind record at Block Island. in 1976, Hurricane Belle came during an El Niño year. All of these storms had developed quite close to the coast.

Note on El Niño

I have very little change here. The Southern Oscillation Index is going to have a big drop in August and the warming of the Pacific is not that great. The difference between the warming tropical Pacific and the cold Atlantic leads to the above idea as far as the Sea Level Pressure pattern goes. There is a vast difference in the look of the Main Development Region compared to last year (which was warm).

In any case, the Sea Level Pressure pattern forecasted in the Pacific and Atlantic is hostile for the Main Development Region, but the worry is that to the north, features can be stronger than average.

My confidence is high given the earlier ideas that were lower than average.

The Verdict

While much less active than last year, as far total ACE, difficult storms are likely to develop near enough to the coast for big challenges. The water is very warm near the U.S. coast and the forecasted ECMWF pressure pattern, with high pressure over Canada like that, counters analogs that are back toward the hurricane hit drought years. High pressure over the Main Development Region should mean less long-track storms that are easy to see coming. Less of a season does not mean a non-season.


There are two things I have been pushing over the years - our ideas on where to look for the highest ACE within the season and the Power and Impact Scale.

I believe that the scale I have developed, incorporating pressure and pressure tendency, is a much better indicator of the impact and total strength that a storm will have over a larger area than the Saffir-Simpson scale. Let's take Ike and Sandy. The scale uses the pressure categories 1-5 and the wind categories 1-5 on the Saffir-Simpson scale to come up with a total 1-10. A rapid deepening storm, more than 3/mb hour, gets an extra point tacked on, 1mb/hour a half point, and vice-versa for weakening. The physical reason for this is that a rapidly deepening storm is indicative of feedback mechanisms working so well that the storm is able to produce the maximum wind it's capable of. Conversely, if weakening rapidly, it's likely not to be able to bring that to the surface.

Ike, at 953 mb, was in the mid-range of Cat 3, "3.5" for pressure. Winds were reported at 110 mph, which is about 2.75 for wind. This made Ike on my scale a 6.25, which is a major hurricane. Gustav was about the same. Do you think for one second 75 years ago before all the categorizing we see now, those storms would not have been recorded as majors? More importantly, they did major damage. By the way, even though it might be technically true by way of the Saffir-Simpson scale, I believe it's not right to claim that the U.S. has not been hit by a major hurricane since 2005. Gustav, Ike, and Sandy all were major impacting hurricanes and had the damage to prove it (though over a larger area). This is why the overall power of the storm in relation to other storms is approximated much better with my scale.

Sandy, at landfall, had a 946 mb pressure (verified by land observations at a barometer that was calibrated to within 0.5 mb several times when I was home at Somers Point, NJ), which is about a pressure of 3.75 on the Saffir-Simpson scale. Sandy was weakening off its peak several hours before, so the pressure is adjusted to 3.25. Winds were at 85 mph, which is a 1.5. Sandy goes down not as a Cat 1 hurricane but a combined 4.75, which is healthy Cat 2 (if we are going to chop it in half). This ranking certainly does it more justice.

While I am not holding my breath about this being adopted, I will from time to time reference it so we can have a better idea of the total picture of the storm. It's the old argument, the slugger (my power scale) or the boxer (the more "proper" Saffir-Simpson scale).