peak of hurricane season Archives

Peak of Hurricane Season is Today!

Today, September 10 is the statistical peak of hurricane season.

NOAA calculates the peak by looking at the number of storms per day in the last hundred years. And September 10th takes the prize with approximately 95 named storms. That’s almost one per year on this date. You would have about a 5% chance of NOT having a named storm in the Atlantic Basin on September 10th, according to this data.

And true to form, today, the Atlantic has two named storms, Lee and Margot, as I write this. However, neither is anywhere near the Caribbean or Gulf of Mexico.

NOAA hasn’t really been collecting hurricane data back 100 years. The chart above is based on 77 years of data, but “normalized” to 100 years to make the frame of reference more intuitive.

The 77-year period extends from 1944 to 2020, starting at the beginning of the aircraft reconnaissance era.

So Far This Year Vs. Average Season

Usually, by September 9, we’ve had eight named storms in the Atlantic Basin. That would be the H storm. However, this year, we’re already on the M storm. That puts us five storms ahead of the average year.

But wait! This year we also had a bonus storm in January. Only after re-analysis did the National Hurricane Center realize that it should have named the storm. But it didn’t. So, we’re really six storms ahead of the average season so far. And that’s far above the average.

*Only two named storms in the Gulf so far this year. Neither has come close to Houston.*

The chart above is updated monthly and does not include the two named storms now in the Atlantic.

Forecast vs. Actual to Date

So, at the mid-point, how does this season compare to predictions? If the second half of the season is anything like the first, we could easily have more named storms and more major hurricanes than predicted by NOAA in its August 10 seasonal update.

Earlier this year, forecasters increased their predictions from a normal season to an above normal season. They predicted 14-21 named storms (winds of 39 mph or greater). We’ve already had 14.

Of those, NOAA said 6-11 could become hurricanes (winds of 74 mph or greater). We’ve had 4 so far (Don, Franklin, Idalia and Lee).

And of those, forecasters said 2-5 could become major hurricanes (winds of 111 mph or greater). We’ve had 3 of those so far (Franklin, Idalia and Lee). Franklin and Idalia reached Category 4 strength. Lee briefly exploded into a Cat 5.

Forecasters have linked storm intensity to sea surface temperatures. When average storms hit very warm waters, they can intensify quickly. And that is exactly what has happened this year.

Here’s a look at sea surface temperature anomalies (departure from normal) around the world.

Virtually everything between Africa and Houston is 1-3 degrees Celsius above normal (1.8 to 5.4 degrees Fahrenheit). Sea surface temperature data is current as of Sept. 9, 2023…just one day before the peak of hurricane season.

Posted by Bob Rehak on September 10, 2023 based on information from NHC.

2203 Days since Hurricane Harvey

Hurricane Season Above Average So Far

NOAA’s National Hurricane Center issues a monthly Atlantic Tropical Weather Summary during hurricane season. For June 2023, it shows above normal tropical cyclone activity and and above normal accumulated cyclone energy (ACE) for the North Atlantic, Caribbean and Gulf of Mexico.

#4 for Year and Counting

Three named tropical storms (Arlene, Bret, and Cindy) formed in the basin during June. The report also shows an unnamed storm in January, that in retrospect appears to have been tropical in strength.

Bret brought tropical-storm-force winds to portions of the Lesser Antilles, while Arlene and Cindy remained over open water and did not impact land.

So far, seasonal activity has been above average based on the 30-year climatology (1991-2020), where a named storm typically forms about once every year in June.

In terms of Accumulated Cyclone Energy (ACE), which measures the strength and duration of tropical storms and hurricanes, activity in the basin so far in 2023 has also been above average compared to the long-term (1991-2020) mean.

Reports on individual cyclones, when completed, are available at the National Hurricane Center website.

Summary Table

Name Dates Max Wind (mph)

———————————————————–

Unnamed STS*

TS Arlene 1-3 Jun 40

TS Bret 19-24 Jun 70

TS Cindy 22-26 Jun 60

———————————————————–

* An unnamed subtropical storm formed in mid January. Exact dates and maximum winds will be provided once the post-storm analysis is complete.

As of this writing on 7/5/23, NHC predicts NO tropical storm activity anywhere in the Atlantic basin for the next seven days.

Predictions Vs. Actual

In May, both NHC and Colorado State University predicted that this tropical storm season would have about normal hurricane activity. Both sources cited conflicting trends as the basis for their predictions. We currently have above-normal sea-surface temperatures throughout most of the Atlantic basin. We also are now under the influence of an El Niño, which tends, in this latitude, to produce wind shear that discourages cyclone formation.

To improve predictions, NOAA has made a number of changes in reporting at the National Hurricane Center. They include new, improved models for hurricane forecasts and storm surge, longer-range hurricane outlooks, an excessive rainfall outlook, inundation mapping down to the street level, and improved data-collection technologies.

Posted by Bob Rehak on 7/5/2023

2136 Days since Hurricane Harvey

Today is Statistical Peak of Hurricane Season

According to the National Hurricane Center (NHC), today is the statistical peak of hurricane season in the Atlantic Basin.

Little Known Facts About Hurricanes: Peak of Season

The NHC has a fascinating page on hurricanes and climatology. Here are some interesting facts I gleaned from it.

*Source: NHC. Peak of season occurs on September 10.*

“The official hurricane season for the Atlantic Basin (the Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico) is from 1 June to 30 November. As seen in the graph above, the peak of the season is from mid-August to late October. However, deadly hurricanes can occur anytime in the hurricane season,” warns the NHC.

Average Number of Storms

In an average season, we get 11 or 12 named storms, six of which become hurricanes and two or three of which become major hurricanes (category 3 or greater).

Twelve storms would get you to the letter L. But so far this year, we’re already on the R storm. And we have three more months to go in the season.

Points of Origin Tend to Shift by Month

The NHC shows where hurricanes tend to form each month of the season. In the first ten days of September, more hurricanes form in the Gulf than at any other time. The NHC shows a whole series of charts like the one below. It’s interesting to see how they change from period to period.

*Source: NHC. Sept. 1-10 and Sept. 11-20 show the greatest number of hurricanes forming in the Gulf.*

Note how few storms formed in the Caribbean compared to the period from October 11 to 20.

*Compared to September 1-10, note how many more storms formed in the Caribbean during October 11-20.*

Track Probabilities Also Shift by Month

The NHC also shows an interesting series of charts that show track probabilities by month. September is the most likely month for storms to track through the Caribbean, into the Gulf and onward to the Texas coast.

In stark contrast, during October, storms are most likely to veer east toward Florida and the East Coast.

Strike Density on Western Gulf Coast

On the Texas Gulf Coast, Galveston has been hit more times than any other county. Harris, Brazoria and Chambers Counties follow closely.

Today’s Five Day Tropical Outlook

As if on cue, the NHC is now tracking seven tropical disturbances (as of 800 AM EDT Thu Sep 10 2020).

The two closest to Texas are highlighted in yellow above. That means they currently have less than a 40% chance of formation.

A large area of disorganized showers and thunderstorms near the Bahamas is forecast to move westward, crossing Florida on Friday and moving into the eastern Gulf of Mexico over the weekend. Upper-level winds are expected to become conducive for some development of this system while it moves slowly west-northwestward over the eastern Gulf of Mexico early next week. Formation chance through 5 days is 30 percent.

Another trough of low pressure has developed over the northeastern Gulf of Mexico and is producing a few disorganized showers and thunderstorms. Some slow development of this system is possible while this system moves westward and then southwestward over the northern and western Gulf of Mexico through early next week. Formation chance through through 5 days is even lower, at 20 percent.

Posted by Bob Rehak on 9/10/2020

1108 Days since Hurricane Harvey

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