ACE

Hurricane Season 2016 Officially Ends, Higher ACE Index

From a record-breaking extremely strong El-Nino last hurricane season, the Atlantic, the EPAC and the Central Pacific this season all were above normal. This was pretty much forecast but Mother Nature fools forecasters all the time. A short summary of the season follows:

For the Atlantic,  2012 was the last time there was an above average season. The Atlantic saw 15 named storms during Hurricane season, 2016. Out of the 15 named storms, the Atlantic basin had 7 hurricanes Alex, Earl, Gaston, Hermine, Matthew, Nicole, and Otto. What surprised many is that out of those 7 hurricanes, 3 of which were major hurricanes – Gaston, Matthew, and Nicole.

Many were wondering would Florida be spared a hurricane this year. After all these years and true to form, Florida had two Tropical Storms – Colin and Julia, and finally, Hurricane Hermine made landfall in Florida, the first since Hurricane Wilma in 2005. The Eastern coast of the US also was battered with South Carolina having landfall with Tropical Storm Bonnie and Hurricane Matthew.

Speaking of Hurricane Matthew, it was the longest-lived storm in the Atlantic and it was also the strongest with maximum sustained winds of 160 MPH, a category 5. Hurricane Matthew made landfall at Haiti, Cuba, and the Bahamas but as a category 4 storm during  the trek of the Eastern Caribbean and the Atlantic.

Lest us not forget, there were other storms away from the US. Tropical Storm Danielle visited Mexico, Hurricane Earl in the Belize and lastly, very late in the season Hurricane Otto in Nicaragua.

So, how do we get a better feel of the hurricane season activity for this year? One method called Index. ACE Index is using a sum of the energy accumulated with all the cyclones (tropical storms, sub-tropical storms and hurricanes) that happened to form within the hurricane season. Calculating ACE is done by using the square of the the wind speed every six hours during the storm’s lifetime. Remember, a tropical depression is below 35 knots and it is not added. Hence, a cyclone that is longer lived will have a higher ACE indices verses a shorter lived cyclone which will have a lower ACE indices.  ACE indices of a single cyclone is windspeed (35 knots or higher) every six hour intervals  (0000, 0600, 1200, 1800 ) or ACE = 10kn2.

Total ACE:

\Sigma = \frac{Vmax^2}{10^4} \ \

* Vmax is estimated sustained wind speed in knots. *

An average seasonal ACE in the Atlantic is between 105 -115 or mean average of 110.

2016 Atlantic ACE
Tropical Cyclone Name
Max Wind Speed (in Knots)
ACE 10kn2
Alex *
75
4.1725
Bonnie *
40
0.1055
Colin
50
1.1350
Danielle *
40
0.4050
Earl
65
1.5450
Fiona *
45
3.0275
Gaston  105 24.2925
Hermine
70
3.0925
Ian
55
2.9575
Julia
35
1.2250
Karl
60
5.8150
Lisa
45
2.2600
Matthew
140
47.9950
Nicole
115
25.2075
Otto
95
6.1600
——–
ACE Total:
132.4350

Please note: Those with red asterisks have Tropical Cyclone Reports versus the Operational Advisories. The TCR’s are more comprehensive in detail. Those without the red asterisks will have the TCR’s in time. The ACE Index numbers may change with each TCR. I will try to update this post at that time.

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2014 Hurricane Season. An El-Niño Year?

Before the 2014 Atlantic hurricane season began, it was touted by most experts to be an “El Niño” year mostly due to some the early indicators. A few things Meteorologists monitor when it comes to tropical development in general include: Wind Shear strength, Sea Surface Temperatures/Deep Sea Temperatures, measuring of the SOI (Southern Oscillation Index) in the case of an El Niño or La Niña, and the MJO (Madden Julian Oscillation). A simplified description of an El Niño is basically an area in the Pacific Ocean that begins to warm up to more than above average sea surface temperatures. An El Niño can cause strong winds to blow eastward over Mexico and help shear off the cloud tops of thunderstorms. This helps to reduce both the number and the intensity of tropical storms and hurricanes that might be trying develop in the Atlantic. Between February-May, just before the hurricane season would begin, there were a series of Equatorial  in the Pacific which allowed for the possibility of a moderate to strong El Niño. While the Kelvin waves did transport the higher than normal sea surface heights, the atmosphere did not follow along with the Kelvin waves and the waves eventually faded away. Recently though, two more eastward moving Kelvin waves were seen via the Jason-2 satellite. Will these two Kelvin waves be the precursor for the El Niño? Even if they do, the El Niño would most likely be a weak to moderate one. kelvin-waves_9_18 Courtesy NASA/JPL-Caltech Another possible indicator of an El Niño is that the shift in the SOI has now been in negative territory. Although this is not a true indicator as of yet, the SOI needs to have sustained negative values below −8. Close but no cigar. soi30 Courtesy: Australia Bureau of Meteorology ******* For the math minded ******** There are a few different methods of how to calculate the SOI. The method used by the Australian Bureau of Meteorology is the Troup SOI which is the standardised anomaly of the Mean Sea Level Pressure difference between Tahiti and Darwin. It is calculated as follows:

SOI = 10 \frac{(Pdiff - Pdiffav)}{SD(Pdiff)} \

where: Pdiff = (average Tahiti MSLP for the month) – (average Darwin MSLP for the month), Pdiffav = long term average of Pdiff for the month in question, and SD(Pdiff) = long term standard deviation of Pdiff for the month in question. The multiplication by 10 is a convention. Using this convention, the SOI ranges from about –35 to about +35, and the value of the SOI can be quoted as a whole number. The dataset the Bureau uses has 1933 to 1992 as the climatology period. The SOI is usually computed on a monthly basis, with values over longer periods such a year being sometimes used. Daily or weekly values of the SOI do not convey much in the way of useful information about the current state of the climate, and accordingly the Australian Bureau of Meteorology does not issue them. Daily values in particular can fluctuate markedly because of daily weather patterns, and should not be used for climate purposes.

*************************************

So what does this mean for this year’s Atlantic hurricane season? Probably not a whole lot. So far there is no empirical evidence either way to back up any claims of a possible El Niño. What is known is that in the Pacific, trains of Tropical cyclones in the Pacific are still developing where as in the Atlantic basin this has been a very slow hurricane season with one tropical storm and four hurricanes, with Hurricane Edouard being a major hurricane, albeit short lived as a major. As the  season is slowly drawing to an end, the remainder of the tropical cyclone development (if any) will most likely be in the Western Caribbean and the Gulf of Mexico with the possibility of development closer to the U.S. Eastern coast. It would be foolish for me to to postulate whether the rest of the Atlantic hurricane season will continue to be as slow as it has been and whether the forecasted El Niño has been the cause (whether it is classified or not). As a stated in an earlier post:

So, how do we get a better feel of the hurricane season activity for this year? One method called Index. ACE Index is using a sum of the energy accumulated with all the cyclones (tropical storms, sub-tropical storms and hurricanes) that happened to form within the hurricane season. Calculating ACE is done by using the square of the the wind speed every six hours during the storm’s lifetime. Remember, a tropical depression is below 35 knots and it is not added. Hence, a cyclone that is longer lived will have a higher ACE indices verses a shorter lived cyclone which will have a lower ACE indices.  ACE indices of a single cyclone is windspeed (35 knots or higher) every six hour intervals  (0000, 0600, 1200, 1800 ) or ACE = 10kn2. Total ACE: \Sigma = \frac{Vmax^2}{10^4} \ \ * Vmax is estimated sustained wind speed in knots. * An average seasonal ACE in the Atlantic is between 105 -115 or mean average of 110. Although technically we are in a Neutral state, this season “almost” seems more like a El-Niño year. An El Niño tends to hinder tropical cyclone development in the Atlantic, due to higher amounts shear. But in a true El-Niño year, you normally will have a very active season in the East Pacific (EPAC), with a few major hurricanes, and a subdued Atlantic.

In the figure below, as of this time frame, the ACE Index for this year is actually lower than last years (36.1200). That said, there is still October and November for the possibility of Tropical Cyclone development. If any Tropical Cyclones do develop, I will add them into the ACE Index accordingly. Secondly, the ACE Index numbers in the chart are from the Operational Advisories. The numbers may change when the Tropical Cyclone Reports are released. A blue asterisk will be placed next to a Storm name when a TCR has been issued.
Addendum: As of 10/11/14, 0000 UTC advisory with Tropical Storm Fay, the ACE Index has now surpassed last years ACE. In addition, recently developed Hurricane Gonzalo now a category 4 hurricane, the ACE Index will continue to rise significantly. This the first time in the Atlantic basin there has been a category hurricane 4 since Ophelia in 2011.

2014 Atlantic ACE
Tropical Cyclone Name
Max Wind Speed (in Knots)
ACE 10kn2
Arthur *
85
6.9475
Bertha *
70
5.5175
Cristobal *
75
7.9225
Dolly
45
0.8050
Edouard *
105
15.6325
Fay *
70
3.5600
Gonzalo *
125
25.9725
Hanna *
35
.2450
——–
ACE Total:
66.6025

As always, please be sure to use the official information from the NHC or your local NWS. Although care has been taken in preparing the information supplied through the Weather or Knot blog, Weather or Knot does not and cannot guarantee the accuracy of it. I am not a professional meteorologist and this post is prepared purely for entertainment purposes.

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2013 Atlantic Hurricane Season: A Busted Forecast

Although the 2013 Atlantic hurricane season has not yet concluded and we still have November to contend with before the season will officially be over, all indicators are beginning to make it obvious that the end of the show is near. If you recall in my July hurricane season forecast , all signals were looking for an active season. All the criteria seemed to fit but for some unknown reason, a big piece of the puzzle has alluded forecasters as to why this years hurricane season was very, very below normal. Yes, the Atlantic basin did have a total of 13 named storms, so in one sense the season has been “active” but there were only 2 hurricanes and both were minimal category 1 hurricanes.  However, 13 named storms does really cannot tell the whole story.

So, how do we get a better feel of the hurricane season activity for this year? One method called Index. ACE Index is using a sum of the energy accumulated with all the cyclones (tropical storms, sub-tropical storms and hurricanes) that happened to form within the hurricane season. Calculating ACE is done by using the square of the the wind speed every six hours during the storm’s lifetime. Remember, a tropical depression is below 35 knots and it is not added. Hence, a cyclone that is longer lived will have a higher ACE indices verses a shorter lived cyclone which will have a lower ACE indices.  ACE indices of a single cyclone is windspeed (35 knots or higher) every six hour intervals  (0000, 0600, 1200, 1800 ) or ACE = 10kn2.

Total ACE:

\Sigma = \frac{Vmax^2}{10^4} \ \

* Vmax is estimated sustained wind speed in knots. *

An average seasonal ACE in the Atlantic is between 105 -115 or mean average of 110. Although technically we are in a Neutral state, this season “almost” seems more like a El-Niño year. An El Niño tends to hinder tropical cyclone development in the Atlantic, due to higher amounts shear. But in a true El-Niño year, you normally will have a very active season in the East Pacific (EPAC), with a few major hurricanes, and a subdued Atlantic.

2013 Atlantic ACE
Tropical Cyclone Name
Max Wind Speed (in Knots)
ACE 10kn2
Andrea
55
1.6175
Barry
40
0.7625
Chantal
55
2.4800
Dorian
50
2.5725
Erin
40
1.5450
Fernand
50
0.6550
Gabrielle
55
1.8150
Humberto
80
8.9375
Ingrid
75
4.9000
Jerry
45
1.9450
Karen
55
2.2675
Lorenzo
45
1.6200
Melissa
55
3.4725
No-Named Storm (AL152013)
45
1.4000
——–
ACE Total:
36.1200

As part of the post-season review, the low pressure system in December(AL152013) was classified as a subtropical cyclone and the ACE Index has been updated to reflect the ACE numbers during it’s short lived status as a subtropical cyclone.

Two notes of interest: One is that of the two hurricanes this year, Humberto was just hours from beating the record for the latest first Atlantic hurricane of the season. Secondly, this will be the 8th year in a row where the Atlantic hurricane season has not had a major hurricane (category 3 or higher). In fact, 10/24/2013 was the 8th anniversary when Hurricane Wilma made landfall on the southwestern side of Florida as a Category three hurricane and headed northeastward and the areas of the Miami-Dade, Broward, and Palm Beach counties were impacted with category two winds. If by at the end of this year hurricane season with no major hurricanes, we will tie the record.

So is there a last hurrah for one or two more storms or is it time to fold the tents and call the season over? Technically, no as the hurricane season does not oficially end until November 30. This does not mean a cyclone cannot develop. It is just that a cyclone developing after the official season is over, is a somewhat rare event, but it is not impossible. Usually any late season storms develop either in the Southwestern Atlantic or more likely in the Caribbean. The two late season cyclones late that come to mind were Sandy (2012) and Mitch (1998). As of yet, it appears that the rest of November will be quiet and although there is a chance development of in the Caribbean due to the , I am somewhat skeptical on that. I won’t rule it out yet but for the moment I just am not convinced this will happen, IMHO.

As always, remember to always keep an eye to the sky and to always stick with official information, either your local  or the NHC

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