Weather456's Tropical Weather Blog

2009 Hurricane Season FAQ

By: Weather456, 3:06 PM GMT on April 25, 2009

Good Saturday to all and as I promise, I answered some of the questions about the upcoming season below.

2009 Hurricane Season FAQ

1. Where will the Bermuda-Azores High be stationed this year?

2. Who is at high risk this year?

3. What is the degree of re-curvature this year?


Well there is no definite position that can be predicted due to the intra-seasonal movements of the high and the transits of frontal troughs that breakdown the high. However, by looking at the mean position and strength we can get an idea of the nature and behavior of the high this summer. Another useful tool is the North Atlantic Oscillation phase.

In June and July, the NAO enters a positive phase with a strong sprawling high pressure making areas such as the Central Caribbean, Yucatan Peninsula and Gulf Coast susceptible to tropical storms and/or hurricanes. In August, the phase is expected to shift to negative causing activity to shift north possible along the Northern Caribbean, Florida and East Coast, with the East Coast at the highest risk. In September, the high becomes more random with storms either re-curving or travelling west north of 15N or 20N.

Keep in mind, this is a general idea and that everyone this hurricane season is at risk and thus, should be prepared.

Re-curvature is dependent on extratropical cyclones’ frontal trough. The more active the extra tropics are during the summer, the more re-curvature expected (2006) and vice versa (2004). Pressure anomalies are indicating that above normal pressures in the subtropics-extra tropics may result in reduce extratropical cyclones and their associated troughs causing storms to move further west under what is expected to be an influential high pressure system this year.

4. How active will the 2009 Hurricane Season be?

Only Mother Nature truly knows. But I expect a slightly above average season with 13 named storms due above normal sea level pressure, below normal rainfall and a neutral NAO. Vertical wind shear and SSTs are favorable this year so we may see more activity closer to home, which troubles me. I think some forecasters are developing El Nino too quickly so I won’t be surprise if we end up with more than 13.

5. Will El Nino, La Nina or Neutral conditions affect this year’s hurricane activity?

Based on current trends and model forecasts, there is an 80 percent chance of neutral conditions this year with a 10 percent chance of El Nino developing and another 10 per cent chance of La Nina re-developing. Even if El Nino develops this summer, the effects will lag months behind. Neutral conditions will have the same effect that it had on the 2008 Hurricane Season by helping to reduce the amount of vertical wind shear over the tropics. This is seen by the below normal wind shear within the subtropical jet for April 2009.

6. How soon can we expect activity in the Atlantic basin?

Last year the Madden-Julian Oscillation was a deciding factor in the start of the hurricane season. I remembered vividly that the MJO was forecast to be favorable across the Eastern Pacific/Western Atlantic between May 26 and June 2 and many models forecasted this upswing wound result in a tropical system in either the Eastern Pacific or Atlantic. This led to the formation of Alma and subsequently Arthur. The MJO was then forecast to return for two weeks starting at the beginning of July, when Hurricanes Bertha and Dolly formed along with Tropical Storm Cristobal.

The GFS expects that the MJO will be favorable over the Western Hemisphere (Eastern Pacific and Atlantic) during the first 2 weeks of May and then become unfavorable over the last two weeks and into the start of the season. The wave then returns in mid-latter June. However, the CFS expects favorable MJO during the start of the season. Atmospheric pressure is expected to be above normal in May and near average in June so based on this, along with climatology and other analog years, mid-latter June seems to be the best time.

It should be noted that coinciding with the upswing in the MJO in the first 2 weeks of May the GFS is developing a system in the Southern Caribbean, similar to what it was predicting in 2008. With the exception of this area, I do feel first signs of development maybe in June.*

7. Was forecasting the 2009 Hurricane season easier/more difficult than previous years?

This year’s forecast had many uncertainties especially with the NAO/MSLP and Sahel Rainfall. Due these uncertainties, a factor of 0 was added to the forecast for these indicators. Only three factors remained somewhat certain this year – ENSO/Vertical Wind Shear, SSTs and continuation of above normal activity/new detection tools. This is the second most difficult season to forecast with 2005 the most difficult and 2008 the easiest.

This FAQ is expected to be updated just before the season starts should conditions change and/or new information becomes available.

Potential Development in May

Question 6 above states it all. The Global Forecast System (GFS) is forecasting an area of disturbed weather to develop over the Southern Caribbean during a MJO upswing in the next 2 weeks. This is rather strange since the season doesn't begin until June 1. The area lacks model support and that far out it’s very difficult to verify.

Another area, not in terms of development, but tropical wave development emerged over Gulf of Guinea last night. This area possesses some of the tropical wave requirements but not enough to sufficiently confirm it.

More on these two features in the upcoming days and weeks. My 2009 Hurricane Season Forecast is schedule for May 16 2009.

2008 Hurricane Season Verification
2008 Retired Storms
2008-2009 Selected Tropical Cyclone Reports by W456

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Gustav, Ike, Paloma and Alma Retired

By: Weather456, 9:48 AM GMT on April 23, 2009

Good Day to all

On 22 April 2009, at the 31st Session of the World Meteorological Organization's Regional Association IV Hurricane Committee, the WMO retired the names Gustav, Ike, and Paloma from its rotating name lists. The names were replaced with Gonzalo, Isaias, and Paulette.

Gustav and Ike

It comes as no surprise that these two hurricanes were retired since they were the two most destructive storms of the season. Gustav developed over the Central Caribbean before rapidly intensifying as it moved towards the northeast. Gustav then slammed into Western Cuba with winds of more than 140 mph. The storm entered the Gulf where it weakened to a category 2 hurricane before moving ashore over central Louisiana. Gustav caused more than a 100 fatalities and 6.6 billion dollars.

Hurricane Ike was the third most destructive hurricane to ever make landfall in the United States. It was the ninth named storm, fifth hurricane and third major hurricane of the season. It was a Cape Verde-type hurricane, as it started as a tropical disturbance off the coast of Africa near the end of August, then tracked south of Cape Verde and slowly developed. On September 1, 2008, it became a tropical storm west of the Cape Verde islands. By the early morning hours of September 4, Ike was a Category 4 hurricane, with maximum sustained winds of 145 mph and a pressure of 935 millibars. That made it the most intense storm in the 2008 Atlantic hurricane season. Ike made its final landfall east of Galveston, Texas, United States as a Category 2 hurricane after devastating the northern Caribbean. Ike caused over 100 fatalities and 32 billion dollars, making it the third most costly hurricane in history behind Andrew and Katrina.

Paloma

The third and most unlikely storm to be retired was Hurricane Paloma which developed across the Western Caribbean in October. Paloma rapidly intensified into a category 4 hurricane as it moved north towards Cuba. On 8 November, it suddenly weakened to a Category 2 hurricane before making landfall near Santa Cruz del Sur, Cuba. Paloma caused 909 million dollars in damage with 1 indirect death.

Paloma was the second most intense November hurricane behind Hurricane Lenny in 1999. Paloma is the fourth time the letter P has been used for a tropical cyclone in the Atlantic Basin. The others were Pablo in 1995, Peter in 2003, and Phillip in 2005. Paloma was also the only hurricane starting with the letter P to be retired in the Atlantic Ocean and to be retired with the least deaths in the Atlantic.

Lack of Hurricane Hanna’s retirement

Hurricane Hanna was thought to be another candidate that would have gotten its named retired due the enormous fatalities in Haiti (over 500). However, that was not so, and the name will be used again in 2014. The only other such occurrence was Hurricane Gordon in 1994 which caused over 1000 deaths and extensive damages in Haiti and Cuba but was not retired due to Haiti’s lack of preparations. It is still yet unknown why Hanna was not retired.

Tropical Storm Alma

On 22 April 2009, the World Meteorological Organization also removed the name Alma from the list of Pacific hurricane names and replaced it with Amanda for the 2014 Pacific hurricane season. Upon being retired, Alma became the first tropical storm in the eastern Pacific basin to be retired, also making it the weakest storm to be retired.


Figure 1 Hurricane Gustav crossing Cuba after strengthening rapidly.


Figure 2 Hurricane Ike approaching Galveston Bay on 13 September 2009.


Figure 3 Hurricane Paloma near peak intensity over the Western Caribbean on 8 November 2009.

2009 Hurricane Season FAQ

My next blog will be around the start of next week and it will focus on some of the questions about the 2009 hurricane season. So far I have compiled 6 questions and answers (which are listed below) from questions already asked. If you have any questions about the upcoming season, feel free to email me via Weatherundeground or leave it here on the blog.

1. Where will the Bermuda High be stationed this year?

2. Who is at high risk this year?

3. What is the degree of re-curvature this year?

4. How active will the 2009 Hurricane Season be?

5. Will El Nino, La Nina or Neutral conditions affect this year’s hurricane activity?

6. How soon can we expect activity in the Atlantic basin?

New Photo

Below is a photo I took last year from the plant of a local vegetable called the Okra. Tell me what you think by rating it.

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An Earth Day Book Review: Encyclopedia of Hurricanes, Typhoons and Cyclones

By: Weather456, 10:39 PM GMT on April 20, 2009

Earlier this year I bought this book to add to my home tropical meteorology library I found the book to very interesting and helpful that I had to share it with you all. The encyclopaedia is great Earth Day gift for anyone who loves the world of hurricanes and I plead guilty to that charge.

The book covers/cross reference about 400 (additional 80 in the new volume) aspects of tropical cyclone meteorology worldwide from Accumulated Cyclone Energy Index to Tropical Storm Zeta and everything in between.

The encyclopaedia also features more than 80 black-and-white photographs and line illustrations; an array of help appendixes; chronology of hurricanes, typhoons and cyclones; a list of sources to track tropical cyclones; a list of named storms; bibliography and a detailed index.

Encyclopaedia of Hurricanes, Typhoons and Cyclones, New Edition is an indispensible resource for students of environmental sciences and others who need current or historical information on tropical cyclones.

About the Aurthor

David Longshore severed as a Public Information Officer and Director of Special Programs at New York Mayor's Office of Emergency Management between 2000 and 2004. Mr Longshore holds a bachelor’s degree in History and English from Amherst College and a master’s degree in security studies from the Naval Postgraduate School in Monterey, California. He is currently the director of the emergency management and homeland security master's program at Metropolitan College of New York.

Below is an excerpt of information found on Hurricane Katrina (2005) and Hurricane Georges (1998).

"The first truly catastrophic TROPICAL CYCLONE to strike the continental United States in the 21st century, Hurricane Katrina remains on the most devastating natural disasters in U.S. history."

“Wind speeds within the EYEWALL were measured at 150 mph and the system was now moving across the northern Caribbean islands of Saint Kitts and Nevis and Antigua. On St. Kitts and Nevis Hurricane Georges’ fury left 85 percent of the houses...”


Amazon.com customers gives the book an average 4.5 star rating and I fully agree with them.

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2008 Hurricane Season Forecast Verification and 2009 Preliminary Outlook

By: Weather456, 11:40 AM GMT on April 18, 2009

2008 Atlantic Hurricane Season Forecast Verification

In reference to my blog entry on 15 May 2008, I predicted 15 named storms, 7 hurricanes and 3 major hurricanes, based on factors such as the El Niño-Southern Oscillation (ENSO), rainfall patterns across Sahel, the North Atlantic Oscillation (NAO), mean sea level pressure, vertical wind shear, sea surface temperatures and continuation of above normal activity.

Actually, the 2008 Hurricane Season recorded 16 named storms, 8 hurricanes and 5 major hurricanes, which I think is pretty good for mid-long range forecast.



Overview of Indicators

El Niño-Southern Oscillation (ENSO)

During El Nino, high SST over the eastern Pacific causes more deep convection there. The resultant outflow aloft enhances westerly wind shear over the Caribbean and western equatorial Atlantic. Consequently, the 200 mb anticyclonic flow necessary for tropical cyclones to develop is reduced. During Neutrals and weak to moderate La Nina, low SSTs over the eastern Pacific suppress deep convection there. The resultant subsidence enhances rising motion and weak to moderate upper level easterlies over the Tropical Atlantic Summer, which favours tropical cyclone development.

Rainfall Patterns over West Sahel and the Subtropical East Atlantic

West Africa represents the birth place of most Atlantic tropical cyclones. It is also the origin of the West African Dust outbreaks known as the Sahara Air Layer. Wetter than normal conditions over Sub-Sahara Africa indicate wetter and more convective tropical waves increasing the temperature gradient between the sea surface temperature and the 700 mb wave axis and enhancing convection. Wetter than normal conditions also indicate reduce dust phenomena during the season. Drier than normal conditions produces hotter waves at 700 mb and as they move over the cooler sea surface temperatures, this creates a temperature gradient that reduces convection. Drier conditions over West Africa means enhanced African Dust.

The North Atlantic Oscillation (NAO)

The Positive NAO index phase shows a stronger than usual subtropical high pressure centre and a deeper than normal Icelandic low. The Negative NAO index phase shows a weaker than normal subtropical ridge centre and weaker than normal Icelandic low. A stronger than normal ridge lowers SSTs due to increase evaporational cooling of winds blowing over the water and due to decrease southerly flow. A weaker than normal ridge implies more ridging in the Central Atlantic and warmer sea surface temperatures over the Atlantic due to increase southerly flow and less cooling effects by evaporation.

In addition to the effects on SSTs, weaker trades favour tropical cyclone activity (negative NAO index) while stronger than normal trades suppresses tropical cyclone activity (positive NAO index). This is because, the circulation needed for tropical waves and other disturbances to be classified as tropical depressions are disrupted under too much northeast wind flow.

Overview of Remaining Factors

Tropical cyclone activity is enhanced (suppressed) when mean sea level pressure is below normal (above normal), vertical wind shear is below normal (above normal), and sea surface temperatures are above normal (below normal).

Continuation of Above Normal Activity since 1995 and New Tools and Technology

Since 1995, Atlantic tropical cyclone activity has been in upward swing.

Depiction of new monitoring and analysis technologies (advanced microwave sounding unit tropospheric temperatures [Brueske and Velden, 2003], QuikSCAT [Atlas et al., 2001], and the cyclone phase diagram analyses [Hart, 2003]) have increased Atlantic tropical cyclone counts by about one additional system per year.

Summary of Conditions during the 2008 Hurricane Season



El Niño-Southern Oscillation (ENSO)

In early 2008, a very strong La Nina was evident but that soon quickly weakened and transitioned to neutral conditions by the end of June. These conditions persisted throughout the hurricane season and since then have trended back towards a cooler episode. Table 2 shows the 10 most active hurricane season between 1950 and 2008. It is clear that neutral episodes occurred in the most active years on record and that was no exception in 2008.



Rainfall Patterns over West Sahel and the Subtropical East Atlantic

African easterly waves vary inter-annually, and these variations have been found to have an impact on the seasonal hurricane frequency. Increases in rainfall over the western Sahel have been associated with more frequent and stronger waves, and with the occurrence of more intense Atlantic hurricanes.

In 2008, stronger than normal tropical waves were noted as early as May and this above normal activity in tropical wave structure and formation led to the remarkable early season Hurricane Bertha. Bertha was the longest lived July hurricane on record, lasting 17 days and the easternmost forming tropical storm and pre-August hurricane. Another notable Cape Verde storm was Hurricane Ike which caused devastation across the Caribbean and Southern United States. Bertha’s and Ike intensity and longevity were most likely supported by strong healthy tropical waves along with other environmental conditions.

The North Atlantic Oscillation (NAO) and Mean Sea Level Pressure

A negative NAO during the 2008 hurricane season contributed to warm sea surface temperatures over the subtropical Atlantic, fewer dust episodes (which coincided with above average Sahel rainfall), below normal sea level pressure and many westward moving tropical cyclones.

In positive NAO, such as 2007, the storms are driven far south and west due to a far eastern but strong Azores-Bermuda Subtropical ridge. In negative-slightly positive NAO such as 2005 and 2004 the storms form further west and generally move towards the north due to a modest centralised high pressure ridge. In 2004, the Bermuda High possessed characteristics of a negative and positive NAO with a modest high sprawling far across the Atlantic. Hurricanes Dolly, Fay, Gustav, Hanna and Ike owe their tracks to this event.

In addition the negative NAO was reflected by the below normal mean sea level pressure which enhanced the likelihood of tropical cyclogenesis.

Vertical Wind Shear and Sea Surface Temperatures

During the 2008 Hurricane Season, 200 mb winds were low and anticyclonic in nature which was a result of the La Nina-Neutral episode experienced and enhanced tropical yclone activity. Sea surface temperatures on the other hand were near average to below average during June and July but were near-above average during the peak months of August and September. This warm anomaly, almost 2 degrees Celsius in some spots within the Main Development Region (MDR), continued through October and November and this helped fuelled the strong late season storms, Omar and Paloma. This was unexpected since sea surface temperatures were forecasted to be near normal levels and resulted in 2 additional major hurricanes than previously predicted.

Continuation of Above Normal Activity and New Tools

Since 1995, activity in the basin has been on a general upswing even for those seasons with El Nino episodes. This may have contributed to 5 major hurricanes and 4 category 4’s during the 2008 hurricane season.

New methods of detecting tropical cyclones may have added a few storms during the season which includes Laura, Marco and Nana. Laura and Nana are examples of open ocean storms which affected shipping lanes during their extratropical phases. With the absence of satellite technology and the more dense surface stations over the Atlantic, these storms may have gone undetected.

The same is true for Marco, which was so small (18.5 km tropical storm forced winds), may have been mistaken for a strong afternoon thunderstorm was it not for satellite imagery.

Conclusion

It is fair to say that many factors conspire together to make 2008 the 5th most active hurricane season in the past 58 years and the 3rd costliest on record behind 2005 and 2004. A neutral ENSO episode resulted in low vertical wind shear which allowed 200 mb anticyclonic winds to form which helped drive the outflow of wet active tropical waves. A negative NAO reduced SAL outbreaks periods, reduce MSLP and helped warm sea surface temperatures which in turn fuelled strong hurricanes especially in the latter part of the season. In additions, new tools and satellite technology may have added a storm or two due to size and remoteness.


Figure 1 Warm (red) and cold (blue) episodes based on a threshold of +/- 0.5oC for the Oceanic Niño Index (ONI) [3 month running mean of ERSST.v3b SST anomalies in the Niño 3.4 region (5oN-5oS, 120o-170oW)], based on the 1971-2000 base period. Source: Climate Prediction Centre.


Figure 2 Percentage of normal precipitation for Northern Africa between 1 May and 30 September 2008 showing the above average rainfall over the West African Sahel Region. Source: Climate Prediction Centre.


Figure 3 Standardize 3 month running mean of the North Atlantic Oscillation (NAO) through March 2009 showing a negative NAO during the summer of 2008. Source: Climate Prediction Centre.


Figure 4 Mean sea level pressure (MSLP) anomaly for the Atlantic basin through 31 August 2008 in hpa/mb. Source: Australia Bureau of Meteorology (BOM).


Figure 5 Mean 200 mb winds for the Atlantic basin through 31 August 2008 in m/s. Source: Australia Bureau of Meteorology (BOM).


Figure 6 Sea surface temperature anomalies for the Atlantic basin for the months of June-November 2008 in degrees Celsius. Source: Unisys Weather Inc.


Figure 7 Tropical Storms Marco (centre), Norbert (bottom left), and the low that would eventually become Odile (bottom) on 6 October 2008. Source: Caption – Wikipedia, Image – NRL Tropical Cyclones.

2009 Hurricane Season Outlook

It is tool early to really get a good idea of what activity is expected in 2009, but preliminary estimates call for 13 named storms 6 hurricanes and 3 major hurricanes based on only 2 indicators at this point: A neutral ENSO and current SSTs which are above 2008 levels. My official forecast will be issued in May.

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First Possible Tropical Wave of the Season

By: Weather456, 6:12 PM GMT on April 14, 2009

I've been monitoring an area of disturbed weather that emerged off the coast just a few hours ago that may possibly the first African easterly wave of the season. Hovmoeller diagrams show a westward propagation of moisture across Africa over the past couple of days and the latest precipitable water loop and visible image loop shows inverted-v patterns and wave like structure in the low level moisture field. In addition 700 mb curvature and vorticity indicates a PV maxima and vorticity over West Africa.

Update

The first possible wave of the 2009 season appears to have emerged from West African earlier today. The last visible images of the day revealed mid-level spin which further supports a wave-like axis near 11W south of 10N. Surface observations and 850 mb vorticity revealed little surface reflection associated with this feature.

In terms of development, there is a very unlikely chance that this feature will develop into anything more than what it is now. The environmental conditions appear favorable near the coast of Africa where the system is currently at. However, for development to occur the system needs to gain latitude where it will meet dry, stable air supported by cool sea surface temperatures and strong vertical shear. Hence, the likelihood of cyclogenesis is very slim.

If the Tropical Prediction Centre confirms this, this will be one, if not, the earliest tropical wave this decade, and will shed new light on the 2009 Hurricane Season which I previously thought would be an average season.

April 15 Update

Analysis and data (stated above) over the past 12-24 hrs revealed that any possible wave-like feature that may have existed is either weak or dissipated at this point, not surprising of course, due climatology. However, I still hold strong, the idea that a weak African Easterly Wave (AEW) existed at least over the continent but somehow fizzled over an oceanic environment, which again is not surprising. My next blog will be next weekend or if any additional suspect waves formed before then.

MSAT visible image valid 12PM AST/EDT April 14 2009


MSAT infrared image valid 6PM AST/EDT April 14 2009



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Blog Returns This Summer/Happy Easter

By: Weather456, 3:15 AM GMT on April 13, 2009

First, I want to say Happy Easter to all and that my blog will be back this summer and hurricane season. I haven't wasted my time away from the blog, actually I have been reviewing the 2008 hurricane season and verifying my pre-hurricane forecast as oppose to the actually forecast, and personally it was a best for me. Also I have completed several tropical cyclone reports that have listed below which you can download in PDF formats.

The protocol this year will be the same as last; discussing areas of concern in the Atlantic on a daily basis unless otherwise. As stated before, I was working on my 2008 Hurricane Season Forecast Verification, which I will issued in the next week or two and my 2009 Atlantic Hurricane Season Outlook on 31 May 2009.

2008-2009 Selected Tropical Cyclone Reports for the Southern Hemisphere

2008_TCR_AU_03U Billy
2009_TCR_AU_09U Ellie
2009_TCR_AU_17U Hamish
2009_TCR_F_10F Innis (14U)
2009_TCR_R_06R Eric
2009_TCR_R_07R Fanele
2009_TCR_R_08R Gael

2008 Atlantic Hurricane Season Verification Preview

In reference to my blog entry on May 15 2008, I predicted 15 named storms, 7 hurricanes and 3 major hurricanes, based on factors such as El Niño-Southern Oscillation (ENSO), rainfall patterns across Sahel, the North Atlantic Oscillation (NAO), mean sea level pressure, vertical wind shear, sea surface temperatures and continuation of above normal activity.

Actually, the 2008 Hurricane Season recorded 16 named storms, 8 hurricanes and 5 major hurricanes. When it came to named storms and hurricanes, I was right on ball but the 5 major hurricanes were unexpected.

There are several factors that explained why the 2008 Hurricane Season was slight more active than my forecast and especially for major hurricanes.

A Neutral Enso
Above Average Rainfall
Lower than normal sea level pressure
Near to below average upper level winds



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The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Weather456's Tropical Weather Blog

About Weather456

With a Bachelors Degree in Environmental Sciences (2009), began tracking tropical storms in 2002 and is now a private forecaster.