News & Blogs
BERMUDA HIGH/ ITS EFFECTS ON HURRICANES
By: ncforecaster, 2:55 AM GMT on April 06, 2007
I have decided to post my third blog entry in the past 24 hours. Each of these entries are focued on three of the most influential atmospheric and climate signals that impact serasonal activity, as well as any perspective hurrcane landfalls. That being said, the following is simply a repost of my April 19th weather 101 series on the "Bermuda High" from last year. As time allows, I will be providing subsequent blog entries all tailored to helping all of us better forecast what may transpire during the upcoming 2007 Atlantic hurricane season. Thanks again for taking the time to read and/or post in my blogs. I look forward to talking with each of you very soon. In the meantime, I want to wish everyone a great Easter weekend to come.)
WHAT IS THE BERMUDA HIGH?
First of all, it derives its name by its very distinct character. Specifically it is a very large area of high atmospheric pressure that sets itself up and becomes firmly entrenched over the Sub-Tropical Atlantic Ocean. Generally, the center of this high pressure area tends to shrink in size (decrease in its intensity) and moves eastward towards the Azores Islands, where it is affectionately referred to as the "Azores High" as well, near the very end of one hurricane season and throughout the winter months. However, the center of this most influential weather system begins to shift back towards the west and intensify (expands in size), as we approach the beginning of a new hurricane season, and as a result plays a very significant role in both hurricane formation, intensity, and their eventual tracks. Generally speaking, it is a semi-permanent area of sub-tropical High Pressure that migrates between about 30 degrees and 40 degrees North Latitude depending on the season. Specifically, it is located further South and East during the winter and early spring closer to the Azores (why it is often called the Azores High as previously mentioned), and moves more to the North and West as we get into the the late spring through the summer and fall months.
HOW DOES IT AFFECT HURRICANE FORMATION AND INTENSITY?
First, we need to understand that high atmospheric pressure pushes air down towards the surface which in turn causes the air to become drier and much warmer. Since this air is now drier and warmer, it suppresses the formation of clouds (which form from moist air rising off the water). Since there are fewer clouds, the sun is able to more directly heat the oceans surface which in turn allows the water temperatures to increase. Naturally, the intensity of the Bermuda High has a big impact on sea surface temperatures in the main breeding grounds for tropical cyclone activity know as the inter-tropical convergence zone or ITCZ. This region is where the vast majority of tropical waves move off the west coast of Africa between about 10 degrees and 30 degrees North latitude. Furthermore, this area of most favorable atmospheric conditions for tropical cyclone genesis extends westward all the way to Central America.
By the time we reach the peak months of hurricane season that begins in August, the Bermuda High being a weather system that stirs the air around the North Atlantic in a huge clockwise circle, has helped create very favorable atmospheric conditions in this region by allowing the waters to bake beneath the relatively clear skies. Consequently, increased sea surface temperatures in this region helps to provide extra fuel for the hurricane wanna-bees moving from east to west off Africa in the general direction of the east and northeastern Caribbean. As a result, the eventual strength of the Bermuda High plays a surprisingly significant role in how much heat energy will be available for both cyclogenesis as well as further intensification after it actually occurs.
HOW DOES IT AFFECT HURRICANE TRACKS?
As we learned in the previous section, this huge area of High Pressure spins the air over the Atlantic in a giant clockwise circle (image a clock). As also alluded to in the previous section, most tropical systems move off Africa in a general westerly direction being steered by the currents of air on the very southern most edge of the Bermuda High. As they move further westward, the strength, size, and location of the Bermuda High determines where they will ultimately go. In most cases, the clockwise circulation will steer storms more Northwards as they begin to reach the western edges of the Bermuda High and push them out to sea before they can impact the U.S. East Coast. However, it is important to realize that this High pressure system isn't stationary, for it is a weather system like any other and can shift more east, west, north, or south and does so in relation to the effects of other storm systems like frontal systems moving off the U.S. Coast which usually acts to weaken the Highs influence and causes it to migrate farther east. In other instances, the Bermuda High can set itself up farther west than normal where the southern and western edges of its clockwise circulation can allow hurricanes to move farther south and west before they make their eventual and inevitable northward turn. This was the specific pattern that was in place during the peak months of the 2004 hurricane season when a record four hurricanes directly impacted Florida. This is also the scenario that makes the Southeast coast of Florida and the Gulf Coast States most vulnerable. In contrast, if the Bermuda High is set up more towards the east during the peak months of the hurricane season, the East Coast of the U.S. is more vulnerable as was the case in 1996 when North Carolina was struck by two hurricanes in the same season and was also the last time a major hurricane made landfall farther north than Ft. Pierce, Fl.
During the hurricane seasons of 2000-2002, the Bermuda High was much weaker and located farther East than normal which acted to deflect all possible hurricanes well out to sea during those three consecutive seasons when each had well above normal tropical cyclone activity, with only hurricane Lili making a landfall in October of 2002 as a category one in La. Overall, it is when the Bermuda High is displaced from its normal location more South and Westward, that it can stretch its most Western edges close to and even over the East Coast States of the U.S. When this particular set-up occurs, the U.S. coastline is left completely vulnerable to hurricanes. This is because a tropical cyclone is a relatively intense low pressure system that cannot penetrate an area of strong high pressure (which is most intense during the summer months coinciding with our hurricane season) and must go around it. As a result, this most unique High Pressure system acts as a buffer and doesn't allow the Northward turn to take place until it impacts some portion of the U.S. Coastline, or keeps hurricane tracks even as far south and west as Central America. To reiterate, the specific location, size, and intensity of the Bermuda High will ultimately determine if and where the next hurricane will strike.
Updated: 2:57 AM GMT on April 06, 2007
ENSO CYCLES IMPACT ON SEASONAL ACTIVITY
By: ncforecaster, 1:21 AM GMT on April 06, 2007
I decided to post my own commentary related to the historical (climatological) data I researched, gathered and subsequently categorized into the two most influential climate factors that impact Atlantic Basin seasonal activity, during a given year. Please see previous blog entry for the statistical analysis itself. I was going to initially wait a few days before writing my commentary. However, I chose to do so earlier (contained in the comment section of my previous blog) when I was afforded the opportunity in response to another bloggers excellent observations regarding the ENSO cycles, posted in that particular blog.
HOW MUCH IMPACT HAS THE ENSO CYCLES (HISTORICALLY) HAD ON SEASONAL ACTIVITY?
During this research, I noticed a few very interesting things relative to how the respective phases of the ENSO cycles affect Atlantic Basin tropical cyclone activity. Here are a few examples I noticed:
1) The El Nino phase has a far greater impact on seasonal activity than does the La Nina phase (as you pointed out as well).
2) The La Nina phase and Neutral phases have similar statistical figures for both total number of named storms, as well as hurricanes for a given season.
3) However, the La Nina's impact is most notable when it relates to the formation of intense (i.e. Major hurricanes). During the period I examined (1950-2006), La Nina seasons averaged one additional major hurricane per year, which is quite significant.
4) The hyperactive and historical 2005 hurricane season skews the data when comparing the Neutral and La Nina phases. In my analysis from last year (posted in a blog on the subject), the 2005 season was the beneficiary of many late season storms (and of unusual intensity for so late in the season). When looking at the ENSO cycle for the respective months, I noticed that the ENSO cycle was moving towards a la Nina beginning with the month of September and intensifying through December. By definition, the 2005 season didn't meet the criteria to be categorized as a La Nina. On the other hand, the rapidly cooling waters in the central equatorial Pacific no doubt helped this season reach previously unprecedented seasonal activity for number of storms and hurricanes (27/15).
5) There is always an exception (aberration so to speak) to almost every rule. Case in point, the 1969 season was extremely active (18/12/5) despite corresponding to an El Nino phase of the ENSO cycle.
In summary, the historical analysis does show slightly enhanced seasonal activity (most significant relative to major hurricane formation) during a La Nina phase of the ENSO cycle, when compared with the Neutral phase. However, there is a very significant reduction in seasonal activity (at all levels) during the El Nino phase, as shown in the charts compared to the Neutral phase.
DOES THE LA NINA PHASE DESERVE THE HYPE IT GETS?
First, the intensity of a typical La Nina event is not as significant (relatively speaking) as the typical El Nino phase of the ENSO cycle. In contrast, the El Nino events are generally much more intense in comparison to the Neutral phase. That being said, one should expect a far greater impact from an El Nino event than that of its La Nina counterpart. Secondly, we understand that these individual phases of the ENSO cycle have their greatest influence on the intensity of the Easterly upper level winds that blow East to West across the East Pacific and into the MDR (Main Development Region) of the Atlantic Basin. Consequently, a La Nina phase allows for a substantial decrease in the amount of wind shear at these upper levels, and thereby enhances the environment for perspective tropical cyclone formation. In short, one should anticipate atmospheric conditions more favorable for increased tropical cyclone development during the La Nina phase, but not close to the degree of impact an El Nino event would have on a particular season. That being said, one must also appreciate the fact that favorable upper level winds is only one of the key elements that must exist for a tropical cyclone to develop and intensify. With that in mind, the AMO cycle is far more influential in determining seasonal activity than the ENSO cycle. Thanks again for the excellent post and I look forward to talking with you again very soon. In the meantime, I want to wish you and everyone else a great rest of the week and Easter weekend to come.:)
Updated: 2:29 AM GMT on April 06, 2007
HURRICANE CLIMATOLOGY/THE HISTORICAL PERSPECTIVE
By: ncforecaster, 7:45 AM GMT on April 05, 2007
I have decided once again to post an updated and slightly revised version of the tropical cyclone climatological data that I had gathered prior to the 2006 Atlantic hurricane season. Naturally, I have retabulated the figures from last March by simply accounting for last seasons activity. In addition, I noticed where I had the 1999 season listed in the incorect ENSO phase which skewed those figures accordingly. That being said, this updated and revised version concentrated on overall seasonal activity should be most beneficial to anyone interested in speculating about how active the 2007 Atlantic hurricane season might be. In compiling all of the following data, I have chosen to simply focus on the period from 1950-2006 (57 years). In doing so, I have listed and categorized the following data in respect to the most influential climate factor that affects seasonal activity (the AMO cycle) and in the chronological order that is most relevant to the upcoming season (i.e. the two active phases of the AMO). Moreover, I have also categorized them according to the corresponding phase of the ENSO cycle (the other most influential climate factor) for those seasons as well. I uaed the official CPC historical record to accuractly categorize the aforementioned.
The ENSO cycle has three phases that can manifest itself during the hurricane season. They are the hurricane friendly La Nina, the Hurricane inhibiting El Nino, and the Neutral phase which is basically reflective of normal influence from this climate component. In each category listed for both the AMO cycles as well as the ENSO cycles, the data is listed by individual hurricane seasons from left to right. The first set of numbers is for total storms (i.e. tropical and subtropical storms). The second number listed separated by hyphens is the number of hurricanes that developed during a particular season. The third number listed is the number of Major hurricanes (category three or greater) that formed during a season as well. To reiterate, my goal in creating this blog is in the hope that I can share this extensive and very time consuming research, so that everyone can use the information listed herein, to better project their own forecasts for the upcoming hurricane season. Most importantly, I want to thank each and everyone of you who has taken the time to read and/or post in my blogs. Likewise, I want to also wish each and every one of you a truly blessed rest of the week, and Easter weekend to come.:)
CURRENT ACTIVE PHASE OF THE AMO (1995-2006)
1995 19/11/5 1998 14/10/3 1999 12/8/5
Totals 45/29/13 (3 years) Averages 15/9.7/4.3
1997 8/3/1 2002 12/4/2 2006 10/5/2
Totals 30/12/5 (3 years) Averages 10/4/1.7
1996 13/9/6 2000 15/8/3 2001 15/9/3
2003 16/7/3 2004 15/9/6 2005 27/15/7
Totals 101/56/28 (6 years) Averages 16.8/9.3/4.7
PREVIOUS ACTIVE AMO (1950-1969)
1950 13/11/8 1954 11/8/3 1955 12/9/6 1956 9/4/2
1961 11/8/7 1964 12/6/6
Totals 68/46/32 (6 years) Averages 11.3/7.7/5.3
Important note: It is imperative that one takes into consideration the fact that the first 10 seasons of this active period (1950-1959) didn't have the capability to detect storms by satellite. Consequently, it is highly likely that many storms went undetected and thus, unaccounted for in the historical record.
1951 10/8/5 1957 8/3/2 1963 9/7/2 1965 6/4/1
Totals 51/34/15 (5 years) Averages 10.2/6.8/3
Important note: This El Nino period got a huge boost from the hyperactive 1969 season that featured the legendary hurricane Camille which devastated the Mississippi coastline as a powerful category five.
1952 7/6/3 1953 14/6/4 1958 10/7/5 1959 11/7/2
1960 7/4/2 1962 5/3/1 1966 11/7/3 1967 8/6/1 1968 8/4/0
Totals 81/50/21 (9 years) Averages 9.0/5.6/2.3
INACTIVE AMO (1970-1994)
1970 10/5/2 1971 13/6/1 1973 9/4/1 1974 11/4/2
1975 9/5/3 1978 12/5/2 1988 12/5/3
Totals 76/34/14 (7 years) Averages 10.9/4.9/2
1972 7/3/0 1976 10/6/2 1977 6/5/1 1982 6/2/1
1986 6/4/0 1987 7/3/1 1991 8/4/2 1992 7/4/1 1993 8/4/1 1994 7/3/0
Totals 72/38/9 (10 years) Averages 7.2/3.8/0.9
1979 9/5/2 1980 11/9/2 1981 12/7/3 1983 4/3/1
1984 13/5/1 1985 11/7/3 1989 11/7/2 1990 14/8/1
Totals 85/51/15 (8 years) Averages 10.7/6.4/1.9
GRAND TOTALS FOR EACH CATEGORY:
Totals 189/109/59 (16 years) Averages 11.8/6.8/3.7
Totals 153/84/29 (18 years) Averages 8.5/4.7/1.6
Totals 267/158/64 (23 years) Averages 11.6/6.9/2.8
ALL STORMS FOR THE ENTIRE PERIOD (1950-2005)
Grand Totals 609/351/152 (57 years) Averages 10.7/6.2/2.7
ACTIVE AMO PHASES
376/228/114 (32 years) Averages 11.8/7.1/3.6
INACTIVE AMO PHASE
233/123/38 (25 years) Averages 9.3/4.9/1.5
CURRENT ACTIVE AMO PHASE (1995-2006)
176/98/46 (12 years) Averages 14.7/8.2/3.8
Updated: 11:01 PM GMT on April 05, 2007
MY THOUGHTS ON DR. GRAYS FORECAST DISCUSSIONS
By: ncforecaster, 2:29 AM GMT on April 04, 2007
My thoughts on Dr. Grays forecast discussions:
I just finished reading Dr. Grays new forecast which very closely resembles my own personal thoughts, and highlights some of the data that I had gathered more than a year ago (on my own) about the correlations between global warming and hurricane activity.
In my own humble opinion, I don't believe there is much, if any correlation between hurricane activity and global warming. That being said, I am still a proponent of finding cleaner and environmentally safer forms of energy where feasible (feel we are way too dependant on foreign sources of oil), just for the record. In short, all of my own very detailed unbiased research into any possible correlations between Global warming and hurricane activity overwhelmingly suggests that it is clearly a result of Natural climate variability. Consequently, I am quite confident that 20 years from now, this will be proven to be the case, once the AMO cycle reverts back to a less active phase.
As I stated in my previous post in response to my good friend Rays extremely thoughtful post, I am hoping to post my updated and slightly revised extensive climatological research that I had gathered for weeks back in March of last year. This data could give us a better idea of what we may expect relative to both hurricane activity, as well as any prospective hurricane landfalls along the U.S. shoreline during the upcoming 2007 Atlantic hurricane season. In the meantime, I want to thank each one of you who takes the time to read and/or post in my blogs. Most important of all, I want to wish every individual in this wonderful community a great rest of the day and week ahead.:)
Updated: 2:30 AM GMT on April 04, 2007
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