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The 2013 Atlantic Hurricane Season is officially over. June 1st-Nov 30th, 2014 for the next.
Number of days since last Hurricane Landfall in US: 537 (Sandy) , in Florida: 3100 (8 y 5 m) (Wilma)
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Ed Dunham

Are Seasonal Forecasts Worthwhile?

Posted: 11:27 AM 24 October 2013
In another Forum, Robbissimo asked some excellent questions that are certainly pertinent to this season:

"I would still like to hear your take on the 8th Anniversary of Wilma, specifically whether predicting the weather and hurricanes in particular is a worthwhile endeavor. Seriously, would anyone have predicted we'd go eight years without a single hurricane? Is it that unusual?"

All good questions that I'm sure others have also considered. The short answer is 'No', I certainly would not have predicted an 8 year hurricane drought for Florida and it is rare to go that long without a landfalling hurricane in the state. Here is a link to a Met Blog that I posted in early May of 2012 that chronicles other long stretches without a hurricane in Florida:

Florida's Next Hurricane

The 'Outlook for 2014' in the 2014 Storm Forum explores the probability that the 2014 season may be even quieter than 2013.

Predicting the weather in general and the characteristics of a specific hurricane is a most worthwhile effort. Any type of warning (Hurricane, Tornado, Flood) usually means that deaths and injuries are reduced.

Meteorology is the youngest natural science - perhaps with 150 years under its belt as a science. Compare that with astronomy with 5,000 years. Weather prediction has improved considerably, but we are still learning about the atmosphere and how to predict its changes. With the exception of summertime showers, local weather forecasts are much better than they were 50 years ago. New technology (radar, satellite, computers) has helped to make forecasts better. Does a forecast for 100% chance of rain fail to verify every now and then? - yes, but the science itself is still young. Do seasonal rainfall/temperature forecasts have merit even though their accuracy is limited? - yes, because agricultural and transportation interests, et al, can use them for planning purposes (and often save money as a result). Do seasonal hurricane forecasts have merit? - I think so, although after this season I'm sure that there will be a considerable amount of discussion and research (and soul-searching) related to that topic. Insurance companies don't really use that data as much as the public is lead to believe - but Emergency Management folks do - again, for resource planning purposes. It doesn't always prove very useful for two reasons: 1) the old adage that 'all it takes is one bad storm during an otherwise quiet season', and 2) the outlook can be way off base (like this year) - which takes us back to 'the science itself is still young'.

To continue to make the forecast and to then have some significant forecast failures usually motivates the science to seek answers in an attempt to improve the next forecast.
ED
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Ed Dunham

Realities

Posted: 12:06 PM 30 August 2013
So far this season there has been six Tropical Storms - which certainly indicates an above average level of activity - but the basin is again quiet at a time when the climatological peak of the season is less than two weeks away. In an average season with 11 named storms, by September 1st there would have been 5 named tropical cyclones and 2 of them would have reached hurricane strength. Many seasonal forecasts for 2013 pointed to another year of high tropical cyclone activity in the Atlantic, but is there enough time left in the season for these forecasts to verify?

As an example, the latest (August 2nd) seasonal forecast from Colorado State University still anticipated 18 named storms this year. With 6 so far, the rest of the season needs 12 more for the forecast to verify, or an average of one named storm per week from September 1st through November 23rd (with 8 of the 12 becoming hurricanes since their forecast also expected 8 hurricanes). Checking the past 60 years (1953-2012), has this frequency ever happened before? The answer is 'Yes', although not very often. In 1969, 13 named storms formed in that time frame; 2005 had 14 and 2010 had 16. Other years that came close include 1953 - 10, 1961 - 10, 1984 - 11, 1995 - 11, 1998 - 10, 2000 - 10, 2001 - 11 and 2012 - 11. In a couple of those years a named storm or two actually developed after November 23rd.

Based on the past 60 seasons, the probability of 12 or more named storms forming in the next 12 weeks (through November 23rd) is 5%.

As noted above, how often is the Atlantic basin this quiet prior to the peak of the season? Once again I looked at the past 60 years to find seasons with no named storms from August 27th through September 2nd - with the following results: 1956, 1959, 1968, 1970, 1987, 1994 and 1997. The probability of occurrence for a quiet week during that timeframe is 11.7% - a little more common than I would have guessed. An Invest area with a low pressure center is about to exit the west African coast and could become a named tropical storm by September 2nd, but it will be close as to whether the system develops by then or a day or two later.

Easterly windshear over tropical central Africa remains uncommonly strong and most of the easterly waves over the continent this season have been disorganized under this constant shear. A band of westerly shear from roughly 15N-20N remains strong in the central Atlantic from 70W eastward to 30W. So far this season, atmospheric conditions are simply not yet supportive for significant tropical cyclone development in the central Atlantic primary genesis area - but that could change and a busy late season is still possible.
ED
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Ed Dunham

Tropical Troubles

Posted: 01:44 AM 09 July 2013
Postscript added 07/10:
Tropical Troubles Tamed
Talk about going zero for three - the TUTT low drifted southwest toward western Cuba and dried up; Chantal has come to a screeching halt south of Jamaica; the trailing wave never fired up.

Chantal as of this writing late Wednesday evening is still faintly spinning in place at roughly the 10/18Z position. Its convective shield has split with the major segment well-removed to the northeast of the former center while some convection still near the center struggles against rather formidable windshear and redevelopment seems highly unlikely although reformation is still a possibilty. I'll revise it to 1 for 4 since the emphasis on storm preparation planning is always sound advice.

Original Blog
The next ten days look quite wet over the Bahamas and Florida peninsula. A TUTT (upper level) low currently centered near northern Andros Island in the Bahamas at 08/04Z is moving slowly westward with an increase in shower activity expected over most of the Florida peninsula later on Tuesday into Wednesday. As the upper low moves into the Gulf of Mexico a persistent blocking ridge should re-establish itself over northern Florida on Thursday into Friday and that ridge is likely to stand generally firm for at least a week.

This pattern is certainly evident in the highly interesting 08/00Z GFS model run. Tropical Storm Chantal, currently racing toward the Caribbean Islands, is projected by NHC to slow down as the tropical cyclone moves into the southern Bahamas late Thursday and creeps into the northern Bahamas by late Saturday - which is all rather compatable with the GFS run. That interesting GFS run stops Chantal (or what ever it may have become by then) on Sunday and starts to nudge the system into east central Florida on Monday and across the peninsula on Tuesday and then the model run sloooowly meanders the system toward and into the north central Gulf coast.

This scenario could produce heavy rains across the Bahamas and the Florida peninsula for a week or more. A rather impressive low-latitude wave is following in the wake of Chantal. If that wave develops - and the GFS suggests that it could - the ridge to the north should still be there and the scenario could repeat itself a little further to the south. Long range model projections of tropical systems often change, so its certainly worth monitoring the tropical Atlantic for the next couple of weeks with emphasis on finalizing a storm preparation plan - just in case its needed.
ED
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Ed Dunham

Active Period / Quiet Period - Doesn't Matter Much

Posted: 02:32 PM 18 May 2013
The Atlantic Basin has been in a cycle of increased tropical cyclone activity since 1995 and that cycle is expected to continue in 2013 with a higher than normal number of tropical storms expected in the basin. In the past three years there were 29 hurricanes but only 3 - Irene in 2011 and Isaac and Sandy in 2012 - that made landfall as a hurricane in the continental United Status (although Sandy was not considered as a landfalling hurricane by NHC, many meteorologists disagree).

The start of the new season will soon be upon us and as of June 1st the entire state of Florida will have gone 2,777 days (7.6 years) without a landfalling hurricane - which is the longest hurricane landfalling drought in the Sunshine State since a 9 year stretch in the 1850s-1860s - and all of this during an active period in the Atlantic basin. But with regard to the frequency of landfalling U.S. hurricanes, does it make any difference if the basin is in an 'active' period or a 'quiet' period? The surprising answer is 'not much at all'. For the state of Florida there is a slightly greater risk during an active phase, but for the entire coastline from Brownsville, Texas, to Eastport, Maine, the risk is actually slightly higher when the Atlantic basin is in a period of lower tropical cyclone activity.

From 1995 - 2012 (active period): 144 hurricanes, 31 U.S. landfalls (21.5%), 9 Florida landfalls (6.3%)

From 1977 - 1994 (quiet period): 91 hurricanes, 22 U.S. landfalls (24.2%), 4 Florida landfalls (4.4%)

During the active period (1995 - 2012) 13 of the 18 seasons had a U.S. hurricane landfall and 5 of those seasons had a landfall in Florida - i.e., 13 seasons had no landfalling hurricane in Florida. During the inactive period of 18 seasons (1977 - 1994) 12 of the seasons had a U.S. hurricane landfall and 4 of those seasons had a landfall in Florida - i.e., 14 seasons had no landfalling hurricane in Florida. Finally, the inactive period also had a long stretch without any Florida hurricane landfalls - from October 12, 1987 to August 23, 1992 - 1,777 days (4.86 years). Although the sample set is small, there seems to be no significant correlation between the number of U.S. landfalling hurricanes and the Atlantic basin cycles of tropical cyclone activity, however, the length of time that Florida has gone without a hurricane landfall increases the probability that the state will experience one this season. With the expectation for another busy tropical season, now is the time to develop (or update) your hurricane preparedness plan.
ED
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Ed Dunham

If You Yell Loud Enough...

Posted: 10:39 AM 07 April 2013
...or perhaps I should say "If a considerable number of folks yell loud enough" common sense just might prevail. From the NHC:

"NOAA broadens definition of hurricane and tropical storm watches and warnings
NOAA’s National Weather Service announced today that, starting June 1, the definitions of hurricane and tropical storm watches and warnings will be broadened to allow these watches and warnings to be issued or remain in effect after a tropical cyclone becomes post-tropical, when such a storm poses a significant threat to life and property. In addition, the NWS would ensure a continuity of service by allowing the National Hurricane Center to issue advisories during the post-tropical stage. These changes were motivated by the special challenges posed by Hurricane Sandy, which was forecast to evolve from a hurricane to a post-tropical cyclone prior to reaching the coast.
“Our forecasters now have more flexibility to effectively communicate the threat posed by transitioning tropical systems,” said Louis W. Uccellini, Ph.D., director of NOAA’s National Weather Service. “Sandy’s forecast was remarkably accurate and under a similar situation in the future, forecasters will be able to choose the best option to underscore the urgency involved”.
This policy change was first proposed during the NOAA Hurricane Meeting this past November and has since been the focus of much discussion in the meteorological and emergency management communities, in forums such as the American Meteorological Society Annual Meeting in January and the National Hurricane Conference in March. This change is also supported by preliminary findings from NOAA’s service assessment on Sandy, which will be released in May.
“I would like to thank everyone for their open and candid feedback on this proposal,” said Rick Knabb, Ph.D., director of NOAA’s National Hurricane Center. “Keeping communities safe when a storm threatens is truly a team effort and this change reflects that collaboration”."
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