What has become of the 2015 Hurricane Season?

8 08 2015

Dale C. S. Destin|

Recently issued updated forecasts for the 2015 hurricane season, which started June 1, reiterated another quiet season is highly likely. The latest set of updated forecasts are similarly calling for this season to be even quieter than 2014 and perhaps be among the top 10 quietest on record.

The updated 2015 ensemble forecast

The updated ensemble or mean forecast is for nine named storms (including Tropical Storm Ana, Bill and Claudette), four becoming hurricanes and one becoming a major (Category 3 or higher) hurricane. On average we get twelve named storms, four hurricanes and three major hurricanes.

2015_HurricaneSeason_Graphic

Our ensemble forecast is based on forecasts from Klotzbach and Gray of Colorado State University (CSU), the National Ocean Atmospheric Administration (NOAA), Saunders and Lea of Tropical Storm Risk.com (TSR) and European Centre for Medium-Range Weather Forecasts (ECMWF).

The indicator of the activity used by meteorologists is the accumulated cyclone energy (ACE) index which is a measurement that takes into consideration the number, strength and duration of tropical cyclones (storms and hurricanes) for the season.

The ensemble ACE index forecast for this season is 44, down from 52 indicated in June and 61.35 below the normal/average. If this forecast verifies, this hurricane season will be the tenth quietest since 1981 and the third quietest since 1995.

The season thus far

TS_Bill_2015-06-16_1955ZWe are two months into the hurricane season and thus far, it has been average, notwithstanding the forecast. May to July has had three tropical storms – Ana, Bill and Claudette.

Damage to property has been minimal; however, there have been eight deaths. The Caribbean including Antigua and Barbuda has been unaffected, thus far (“knock wood”).

Ana was a preseason storm and now holds the record for the earliest tropical cyclone to strike the United States. Antigua has never had a tropical cyclone in May but had a hurricane in January 1954 and March 1908.

Why is a quiet season expected?

El Nino is expected to be the main cause of a quiet season. El Nino has strengthened over the past months and has reached the threshold to be categorized as strong.

History has shown that the stronger an El Nino,, the more difficult it is for tropical cyclones to form over the Atlantic. This year we could see what is referred to as a super (strong) El Nino which would make it super difficult for tropical cyclones to form.

Past times have also shown that cool sea surface temperatures (SSTs) across the tropical North Atlantic (TNA) makes it hard for tropical cyclone formation. As of July, SSTs in the TNA were around 0.5 °C below average; hence, cool unfavourable tropical cyclone conditions exist and should remain this way for much of the next three months.

PA-Atl_SSTs_Jun-Jul_2015

Another limiting factor for tropical cyclone formation is the more than usual flow of very dry, dust Saharan air across the TNA. This almost makes it impossible for tropical cyclone to form in their favourite area – between Africa and the Caribbean. However, it is uncertain if this flow will continue.

500MB_RH1

Combined, we may be witnessing one of those rare occasions when all the ingredients are in place to cause one of the quietest hurricane seasons on record.

Probability of Antigua being hit by a hurricane

Based on the ENSO record dating back to 1950, we have never taken a hit from a tropical storm or hurricane during an El Nino episode that has occurred over any part of the hurricane season, and this year is expected to be no different (“knock wood”).

The probability of Antigua being hit by a hurricane annually appears to vary depending on the phase of the Atlantic. However, the overall probability is 28%, based on the period 1981-2010.

According to Klotzbach and Gray, the best similar/analogue years to June-July 2015 hurricane season are 1965, 1972, 1982, 1987 and 1997. Of these years, only Erika brushed us in 1997. Thus, based on similar years, the probability of Antigua being affected this year, by a storm or hurricane, is around 18%, an increase of 3% from the June and the same as what was issued in April.

Don’t be caught off guard

Quiet season or not, we cannot let our guards down. Recall last year’s season was quiet, yet we were rough up by Hurricane Gonzalo. Stay prepared especially since we are in the peak of the hurricane season, August-October.

The hurricane season runs from June 1 to November 30 each year.

Follow us also @anumetservice, facebook and tumblr to keep updated with weather & climate info for the protection of life, property, livelihood & the enhancement of the economy.

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The 2015 Hurricane Season Forecast

2 06 2015

Dale C. S. Destin |

Recently issued forecasts for the 2015 hurricane season, which starts today, indicate another quiet season is most likely. The latest set of forecasts indicates that this season could be even quieter than 2014 and perhaps be among the quietest since 1981.

The 2015 ensemble forecast

The ensemble or mean forecast is for nine named storms (including Tropical Storm Ana), four becoming hurricanes and one becoming a major (Category 3 or higher) hurricane. On average we get twelve named storms, 6 hurricanes and 3 major hurricanes.

HurricaneSeasonForecast2015

Our ensemble forecast is based on forecasts from Klotzbach and Gray of Colorado State University (CSU), the National Ocean Atmospheric Administration (NOAA), Saunders and Lea of Tropical Storm Risk.com (TSR), the United Kingdom Met Office (UKMET), European Centre for Medium-Range Weather Forecasts (ECMWF), Weather Services International (WSI) and Pen State University (PSU).

A better indicator of the activity for the season is the accumulated cyclone energy (ACE) index which is a measurement that takes into consideration the number, strength and duration of tropical cyclones for the season.

The ACE index ensemble forecast for this season is 52. If this forecast verifies, this hurricane season will be the tenth quietest since 1981 and the third quietest since 1995, when the hurricane season went to an active phase.

Why is a quiet season most likely?

El Nino is expected to be the main cause for a quiet season. Basically all the climate models are forecasting El Nino to persist through the hurricane season and keep atmospheric conditions difficult for tropical cyclone formation across much of the Atlantic. Cooling sea surface temperature across the tropical North Atlantic will also hinder tropical cyclone formation.

However, it is not a 100% certainty that we will have a quiet season. We are still in the time of the year when there is very little skill in predicting El Nino. Therefore, notwithstanding what is being said by the models, there is a slight chance of an above normal season; there is also a slight chance of an even quieter season than forecast; it all depends of the eventual strength of El Nino.

It must also be kept in mind that the May seasonal forecasts only possess modest skill in predicting the eventual hurricane season. The early August forecasts, which show the best skill, are the ones to look forward to next.

New normal?

There is a growing consensus that we may have seen the end of a high-activity/active hurricane season era, which started in 1995, and the start of a new low-activity/quiet one, which could last for the next 20-30 years. Thus, for the next several decades, the quiet activity for the past two years could become the norm.

NOAA has indicated that the “current configuration of [sea surface temperatures] SSTs in the Atlantic Ocean… are suggestive that the [Atlantic Multi-Decadal Oscillation] AMO may no longer be in the warm phase” which is synonymous with a high-activity era.

Meanwhile, TSR has continued to indicate that “should this [there] forecast verify… it would imply that the active phase for Atlantic hurricane activity which began in 1995 has likely ended.”

According to CSU, “[the] twelve-month running average values of the [AMO] index are currently at their lowest levels since 1994, when the AMO was in a negative phase” or when we were in the last low-activity era.

This is good news for Antigua and likely the rest of the Caribbean and the wider Atlantic Basin. The fewer the number of tropical cyclones, the less often we will be impacted by tropical cyclones.

Probability of Antigua being hit by a hurricane

The probability of Antigua being hit by a hurricane annually appears to vary depending on the phase of the Atlantic. The probability of being hit by at least one hurricane is around 28%, based on the period 1981-2010. However, during the last low-activity era – 1962 to 1994, the probability was around 14%. While for the high-activity era – 1995 to 2014, the probability increased to around 36%.

Of some comfort, based on ENSO record dating back to 1950, we have never been hit by a hurricane during an El Nino episode that has occurred over the whole or part of a hurricane season.

According to Klotzbach and Gray, the likely best similar/analogue years to the upcoming 2015 hurricane season are 1957, 1965, 1972, 1982, 1987 and 1997. Of these years, we were only brushed by Erika in 1997. Thus, based on similar years, the probability of Antigua being hit this year is about 15%, a decrease of 3% from the April forecast.

Don’t be caught off guard

The 2014 hurricane season produced eight named storms, six hurricanes and two major hurricanes. The ACE index total was 66, the fourth lowest since 1995. It was a quiet year for many but not Antigua, as we were hit by Hurricane Gonzalo.

Gonzalo serves as a perfect reminder that notwithstanding a quiet season, it only takes one hurricane to make it an active season for us. Hence, quiet season or not, the same preparations are required each year for the hurricane season, which runs from June 1 to November 30.

Follow us also @anumetservice, facebook and tumblr to keep updated with weather & climate info for the protection of life, property, livelihood & the enhancement of the economy.





The 2015 Hurricane Season Early Forecast

11 04 2015

By Dale C. S. Destin |

Early forecasts just issued for the upcoming 2015 Atlantic hurricane season indicate another quiet season is likely. The forecasts indicate that the 2015 season could be even quieter than 2014 and perhaps be the quietest since the middle of the 20th century.

Early 2015 consensus forecast

The consensus based on forecasts from Klotzbach and Gray of Colorado State University and Saunders and Lea of Tropical Storm Risk.com (TSR) calls for nine named storms, four becoming hurricanes and two becoming major (Category 3 or higher) hurricanes.

EarlyHurricaneSeasonForecast2015

A better indicator of the activity for the season is the accumulated cyclone energy (ACE) index which is a measurement of the strength and duration of each tropical cyclone. Summing together the ACE of each cyclone, provides a snapshot of how active the season is likely to be outside of just the number of storms.

This year, the consensus forecast calls for an ACE index total of 48. If this forecast pans out, the 2015 hurricane season would be quieter than last year’s and the third quietest since 1995, when the hurricane season went from a quiet phase to an active one.

End of Atlantic active phase?

Around 1995, the Atlantic hurricane season went from a quiet phase, when the average annual number of named storms increased from 9 to 15. Questions are now being raised in the tropical cyclone community as to whether we have come to the end of this active phase.

According to Saunders and Lea, “should the…forecast for 2015 verify, it would mean that the ACE index total for 2013-2015 was easily the lowest 3-year total since 1992-1994, and it would imply that the active phase of Atlantic hurricane activity which began in 1995 has likely ended”.

However, before we burst open the bubblies in celebration of fewer hurricanes for the next few decades, it must be stressed that the ability to accurately forecast an upcoming hurricane season from April, over one and a half months before the start of the hurricane season, is very low. The next set of forecasts, with better skill, will by out by June 1.

Factors pointing to a quiet season

Although the April seasonal forecasts are very low skilled, there are two already occurring phenomena present that are notorious for producing quiet Atlantic hurricane seasons. These are El Nino and a positive North Atlantic Oscillation (NAO). These are the main factors cited for the projected quiet season.

Probability of Antigua being hit by a hurricane

The probability of Antigua being hit by a hurricane annually appears to vary depending on the phase of the Atlantic. Based on the period 1981-2010, the climatological probability of being hit by at least one hurricane is around 28%. However, for the Atlantic hurricane season quiet phase – 1962 to 1994, the probability was around 14%. While for the active phase – 1995 to present, the probability increased to around 36%.

Interestingly, based on ENSO record dating back to 1950, we have never been hit by a hurricane during an El Nino episode that has occurred over the whole or part of a hurricane season.

On the other hand, we have been hit by nine hurricanes during 24 La Nina episodes. By Poisson distribution, this equates to around a 31% probability of us getting hit by at least one hurricane during La Nina.

According to Klotzbach and Gray, the likely best similar/analogue years to the upcoming 2015 hurricane season are 1957, 1987, 1991, 1993 and 2014. Of these years, we were only hit in 2014 by Gonzalo. Thus based on similar years, the probability of Antigua being hit this year is about 18%.

Good news and bad news

There is an Antiguan saying: “de same stick that hit the wild goat will also hit the tame one.” El Nino and the positive NAO will likely “hit” the hurricane season, resulting in suppressed activity. However, these same phenomena will likely “hit” our rainfall activity, resulting in suppressed rainfall and continued drought.

2014 hurricane season and lessons learnt

The 2014 hurricane season produced eight named storms, three hurricanes and two major hurricanes. The ACE index total was 66, the fourth lowest since 1995. It was a quiet year for many but not Antigua as we were hit by Hurricane Gonzalo.

Gonzalo serves as a perfect reminder that notwithstanding a quiet season, it only takes one hurricane to make it an active season for us. Hence, quiet season or not, the same preparations are required.

Our next blog on this topic will be on June 2.

Follow us also @anumetservice, facebook and tumblr to keep updated with weather & climate info for the protection of life, property, livelihood & the enhancement of the economy.








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