FORECAST OF ATLANTIC HURRICANE ACTIVITY FOR OCTOBER 2005 AND SEASONAL UPDATE THROUGH SEPTEMBER

 

The 2005 Atlantic basin hurricane season has already been one of the most active and is already the most destructive season on record.  We project that October will continue the trend of above-average activity that we have witnessed in the preceding four months of the hurricane season.

 

(as of 3 October 2005)

 

 

 

By William M. Gray1 and Philip J. Klotzbach2

 

with special assistance from William Thorson3

 

 

 

This forecast as well as past forecasts and verifications are available via the World Wide Web at http://hurricane.atmos.colostate.edu/Forecasts


Brad Bohlander and Emily Wilmsen, Colorado State University Media Representatives, (970-491-6432) are available to answer various questions about this forecast

 

 

 

Department of Atmospheric Science

Colorado State University

Fort Collins, CO 80523

Email: barb@atmos.colostate.edu

 

 

________________________________

1Professor of Atmospheric Science

2Research Associate

3Research Associate

 

 


ABSTRACT

 

Information obtained through 30 September 2005 shows that we have already experienced a very active hurricane season in the Atlantic basin.  The season has already accumulated 183 NTC4 units which makes it the seventh most active full season since 1950.  In an average season, about 80 NTC units occur before the end of September.

 

Our October-only forecast calls for three named storms, two hurricanes, one major hurricane and NTC activity of 30 which is well above the mean October-only average value of 18.  We expect that by the time the 2005 hurricane season is over, we will witness seasonal tropical cyclone activity at near-record levels.  A seasonal verification of all 2005 activity will be issued on Friday, November 19. 

 

 

2005 ATLANTIC BASIN SEASONAL HURRICANE FORECAST AND END OF SEPTEMBER UPDATE

 

 

Full Season Tropical Cyclone Parameters and their 1950-2000 Climatology (in parentheses)

Full Season Adjusted 5 Aug. 2005 Forecast

Observed Activity Through September

 

Updated October-only Forecast

 

Full Season Adjusted 3 Oct. 2005 Forecast

Named Storms (NS) (9.6)

20

17

3

20

Named Storm Days (NSD) (49.1)

95

85

13

100

Hurricanes (H) (5.9)

10

9

2

11

Hurricane Days (HD) (24.5)

55

35

6

40

Intense Hurricanes (IH) (2.3)

6

5

1

6

Intense Hurricane Days (IHD) (5.0)

 

18

 

11.75

 

1

 

13

Net Tropical Cyclone Activity (NTC) (100%)

 

235

 

183

 

30

 

215

 

 

 

Acknowledgment


We are grateful to the National Science Foundation (NSF) and Lexington Insurance Company (a member of the American International Group (AIG)) for providing partial support for the research necessary to make these forecasts.  We also thank the GeoGraphics Laboratory at Bridgewater State College (MA) for their assistance in developing the Landfalling Hurricane Probability Webpage (available online at http://www.e-transit.org/hurricane).

 

The first author gratefully acknowledges valuable input to his CSU research project over many years by former graduate students and now colleagues Chris Landsea, John Knaff and Eric Blake.  We also thank Professors Paul Mielke and Ken Berry of Colorado State University for much statistical analysis and advice over many years. 

________________________________

4NTC is a combined measure of the yearly mean of six indices (NS, NSD, H, HD, IH, IHD) of hurricane activity as a percent deviation from the 1950-2000 year average. 


VERIFICATION OF INDIVIDUAL AUGUST AND SEPTEMBER MONTHLY FORECASTS

 

 

Our forecast and verification of August-only hurricane activity made in early August – a forecast that verified remarkably well

 

 

Tropical Cyclone Parameters and 1950-2000 August Average (in parentheses)

August 2005 Statistical Forecast

 

Adjusted August 2005 Forecast

 

 

August 2005 Verification

Named Storms (NS) (2.8)

3.2

5

5

Named Storm Days (NSD) (11.8)

12.1

20

21

Hurricanes (H) (1.6)

1.3

3

2

Hurricane Days (HD) (5.7)

6.7

10

7

Intense Hurricanes (IH) (0.6)

0.9

1

1

Intense Hurricane Days (IHD) (1.2)

2.8

3

2.5

Net Tropical Cyclone Activity (NTC) (26%)

 

33.7

 

50

 

42

 

 

 

 

 

Our forecast and verification of September-only hurricane activity made in early September – another successful forecast

 

 

Tropical Cyclone Parameters and 1950-2000 September Average (in parentheses)

September 2005 Statistical Forecast

Adjusted September 2005 Forecast

 

September 2005 Verification

Named Storms (NS) (3.4)

2.7

5

5

Named Storm Days (NSD) (21.7)

17.4

31

36

Hurricanes (H) (2.4)

3.0

4

5

Hurricane Days (HD) (12.3)

9.4

22

18

Intense Hurricanes (IH) (1.3)

1.7

2

2

Intense Hurricane Days (IHD) (3.0)

0.0

6

3.5

Net Tropical Cyclone Activity (NTC) (48%)

 

54

 

80

 

73

 

 


1                    2005 Atlantic Basin Tropical Cyclone Activity through September

 

As of the end of September, 2005 has had seventeen named storms, nine hurricanes and five major hurricanes.  Three major hurricanes have made United States landfall (Dennis, Katrina and Rita), and Ophelia struck the North Carolina coastline (although the eye passed just offshore) as a Category 1 storm.  Hurricane Katrina became the most destructive storm on record after coming ashore in SE Louisiana as a Category 4 storm and devastating the Louisiana, Mississippi, and Alabama coastline.  Table 1 displays the 2005 tropical cyclone statistics for the Atlantic basin through the end of September, and Figure 1 displays the tracks of these tropical cyclones. 

 

            Table 1:   Observed 2005 tropical cyclone activity through September.

 

 

Highest

Category

 

 

Name

 

 

Dates

Peak Sustained Winds (kts)/lowest SLP (mb)

 

 

NSD

 

 

HD

 

 

IHD

 

 

NTC

TS

Arlene

June 9-11

60 kt/989 mb

2.50

 

 

2.6

TS

Bret

June 29-29

35 kt/1002 mb

0.50

 

 

1.9

TS

Cindy

July 5-6

60 kt/992 mb

1.25

 

 

2.2

IH-4

Dennis

July 5-11

130 kt/930 mb

5.75

4.00

2.00

23.1

IH-4

Emily

July 12-21

135 kt/929 mb

9.25

6.75

3.75

32.0

TS

Franklin

July 22-29

60 kt/997 mb

8.00

 

 

4.5

TS

Gert

July 24-25

40 kt/1005 mb

1.00

 

 

2.1

TS

Harvey

Aug. 3-8

55 kt/994 mb

5.50

 

 

3.6

H-2

Irene

Aug. 7-8, Aug. 11-18

85 kt/975 mb

8.75

2.75

 

9.4

TS

Jose

Aug. 22-23

45 kt/1001 mb

0.50

 

 

1.9

IH-5

Katrina

Aug. 24-30

150 kt/902 mb

6.00

4.25

2.50

25.1

TS

Lee

Aug. 31-31

35 kt/1007 mb

0.25

 

 

1.8

IH-3

Maria

Sep. 2-10

100 kt/960 mb

7.75

4.25

0.25

18.2

H-1

Nate

Sep. 6-10

80 kt/979 mb

4.75

2.00

 

7.5

H-1

Ophelia

Sep. 7-18

80 kt/979 mb

11.00

5.25

 

11.9

H-1

Philippe

Sep. 18-23

70 kt/985 mb

5.75

1.75

 

7.7

IH-5

Rita

Sep. 18-24

150 kt/897 mb

6.25

4.25

3.25

27.7

Totals

17

 

 

84.75

35.25

11.75

183.1

 

 

1.1    2005 U.S. Landfalling Storms

 

Figure 2 displays the U.S. landfalling storms for the 2005 hurricane season as of September 30.

 

Tropical Storm Arlene made landfall just west of Pensacola, Florida on June 11 with maximum sustained winds at landfall estimated at 60 miles per hour.  One person drowned in heavy surf kicked up by Arlene, but little damage was reported from the system. 

 

Tropical Storm Cindy made landfall near Grand Isle, LA as a strong tropical storm with maximum sustained winds at landfall estimated at 70 miles per hour.  Three individuals’ deaths were attributed to Cindy.  No damage estimates are available at this time. 


Figure 1: 2005 Atlantic basin tropical cyclone tracks through September. 

Figure 2: Tropical cyclones making U.S. landfall (TS Arlene, TS Cindy, Category 3 Hurricane Dennis, Category 4 Hurricane Katrina and Category 3 Hurricane Rita) through September.  Although Ophelia did not technically make United States landfall, it buffeted the Outer Banks with hurricane-force winds for several hours.  A solid line denotes a tropical cyclone of hurricane intensity, and a dashed line indicates a tropical cyclone of tropical storm intensity. 


Hurricane Dennis made landfall near Pensacola, Florida on July 10 as a Category 3 hurricane with estimated winds at landfall of 120 miles per hour.  Dennis is estimated to have done $3-5 billion dollars in insured damage.  10 people are reported to have died from Dennis in the United States. 

 

Hurricane Katrina made its first landfall as a Category 1 hurricane on August 25 near Hallandale, Florida causing approximately $600 million dollars in insured damage.  Estimated winds at the system’s first landfall were near 80 miles per hour.  The system then drifted southwest into the Gulf of Mexico and intensified into a Category 5 hurricane.  Katrina made its second landfall near Buras-Triumph, Louisiana on August 29 as a Category 4 hurricane with estimated winds of 145 mph.  It made a second landfall near Waveland, Mississippi as a Category 3 hurricane with estimated winds of 125 mph.  Katrina became the most damaging and destructive hurricane on record in the United States with estimates of insured damage nearing $100 billion dollars.  New Orleans was devastated by the storm with tremendous flooding occurring in the city, and most property along the western Mississippi coastline was either damaged or destroyed.  The current death toll from the system is 1140. 

 

Hurricane Ophelia brushed by the Outer Banks of North Carolina as a Category 1 hurricane.  Although the eye of the storm did not pass over land, the system buffeted the Outer Banks with hurricane-force winds for several hours, and there was considerable damage in several coastal counties.  Estimates of insured damage from the system are approximately $800 million dollars.  There were no direct deaths reported from the system.

 

Hurricane Rita brushed by the Florida Keys while intensifying into a hurricane on September 20.  It rapidly intensified into a Category 5 hurricane while moving into the Gulf of Mexico and became the third strongest hurricane on record in the Atlantic basin when its central pressure dropped to 897 mb.  It weakened somewhat before landfall and came ashore in Cameron Parish, Louisiana as a Category 3 hurricane on September 24 with maximum sustained winds estimated at 120 miles per hour.  This landfall position is within a few miles of where Category 4 Hurricane Audrey came ashore on June 26, 1957.  70 deaths have so far been attributed to Rita, and initial insured damage estimates are between $2.5-$7 billion dollars. 

 

2                    Predictions of Individual Monthly Atlantic TC Activity

 

Our Colorado State University research project has shown that a sizable portion of year-to-year variability of Atlantic tropical cyclone (TC) activity can be hindcast with skill significantly exceeding climatology.  These forecasts are based on a statistical methodology derived from 55 years of past global reanalysis data and a separate study of prior analog years which have had similar global atmosphere and ocean precursor circulation features to this year.  Qualitative adjustments are added to accommodate additional processes which may not be explicitly represented by our statistical analyses.  We believe that seasonal forecasts must be based on methods showing significant hindcast skill in application to long periods of prior seasonal and monthly data. 

 

An aspect of our climate research besides our seasonal forecasts is the development of TC activity predictions for individual months.  On average, August, September and October have about 26%, 48%, and 18% or 92% of the total Atlantic basin NTC activity.  Initial August-only forecasts have now been made for the last six seasons.  September-only forecasts have now been made for the last four seasons, and October-only forecasts have now been made for the last three seasons. 

 

There are often monthly periods within active and inactive hurricane seasons which do not conform to the overall season.  To this end, we have recently developed new schemes to forecast August-only, September-only and October-only Atlantic basin hurricane activity by the beginning of each respective month.  These efforts have recently been documented in papers by Blake and Gray (2004) for our August-only forecast and by Klotzbach and Gray (2003) for our September-only forecast – see the references at the end.

 

Quite skillful August-only, September-only and October-only prediction schemes have been developed based on 51 years (1950-2000) of hindcast testing using a statistically independent jackknife approach.  Predictors are derived from prior month, usually June and July NCEP global reanalysis data for all three (August-only, September-only and October-only) individual monthly forecasts and include August’s data for the early September update of the September-only and October-only forecasts.  September data is included for the early October update of the October-only forecast.  Table 2 gives an outline and timetable of the different forecasts and the verifications we issue after the end of each month. 

 

2.1    Independent October-only Statistical Forecast

 

Through examination of the NCEP/NCAR reanalysis, we have discovered five predictors that in combination explain about 60% of the October cross-validated variance in Net Tropical Cyclone (NTC) activity for the hindcast period 1950-2001.  We are currently unable to find combinations of predictors that explain large amounts of variance for the individual tropical cyclone parameters (i.e., named storms, hurricane days, etc.).  Therefore, our October forecast consists of predicting NTC and consequently increasing or decreasing October’s values for the other parameters accordingly.  For example, if October NTC was 150 percent of normal, and a typical October had two named storms, we would forecast three named storms for October. 

 

Table 3 lists the five October-only predictors with their location and sign for enhanced TC activity, and Figure 2 displays these predictors on a map. 

 

Table 4 lists the value of each October-only predictor and whether its 2005 value indicates above or below-average October-only TC activity. 

 

Table 2:  Timetable of the issuing of our after-July monthly forecasts (in early August, in early September, and early October), the times of their verification, and the dates of seasonal updates.  Note that we make three separate October-only forecasts; two separate September-only forecasts, and one separate August-only forecast.  Seasonal updates are issued in early September and early October.

 

 

Times of Forecast

Based on Data Through

 

 

 

Forecasts

 

 

Early

August

July

August Forecast

September Forecast

October Forecast

Full Season Forecast

Early September

August

August Verification

September Forecast

October Forecast

Remainder of Season Forecast

Early

October

September

 

September Verification

October Forecast

Remainder of Season Forecast

 

 

 

 

 

 

 

Table 3: Meteorological predictor and its location for the October-only forecast.  A plus (+) means that positive values are associated with increased hurricane activity, and a minus (-) indicates that negative values of the predictor are associated with increased hurricane activity. 

 

Name of Predictor

Location

1) July-August SLP (-)

(12.5-27.5ºN, 15-45ºW)

2) July-August 200 mb U (+)

(35-47.5ºS, 160ºE-155ºW)

3) Previous November SLP (-)

(45-65ºN, 115-145ºW)

4) August SST (+)

(22.5-35ºN, 120-150ºE)

5) September 200 mb U (+)

(37.5-47.5ºS, 0-30ºW)

 

Figure 2:  Predictors utilized for the October-only forecast which employs meteorological data through September.  Numbers of each area are keyed to the predictor description given in Table 3. 

 

 

 

Table 4:  Values of meteorological parameters for the October-only forecast. 

 

 

Name of Predictor

Parameter Values in Standard Deviations (SD)

Indication for Above or Below-Average Activity

1) July-August SLP (-)

+0.2 SD

Slightly Below

2) July-August 200 mb U (+)

-0.3 SD

Slightly Below

3) Previous November SLP (-)

+0.7 SD

Below

4) August SST (+)

+0.8 SD

Above

5) September 200 MB U (+)

+0.5 SD

Above

 

Three out of five October predictors are negative.  However, two of these predictors are only weakly negative, and our early August forecast for October indicated above-average activity.  We also believe that the current favorable conditions are likely to last for the remainder of the 2005 hurricane season.  We have kept our October forecast the same as it was in early September.  We continue to call for well above-average October activity with an NTC of about 175 percent of the typical October value.  In round numbers, we are forecasting 3 named storms, 2 hurricanes, 1 intense hurricane and an NTC of 30 for October. 

 

Table 5 displays a summary of this year’s hurricane activity through September and our projection for the rest of the season.  We expect October activity to be above its climatological average.  We assume no activity in November. 

 

Table 5:  Summary of hurricane activity through September 2005 and projected hurricane activity for the remainder of the year. 

 

Tropical Cyclone Parameters and 1950-2000 Full Season Climatology (in parentheses)

Observed TC Activity Through September

Updated October Forecast

Updated Full Season Forecast

Named Storms (NS) (9.6)

17

3

20

Named Storm Days (NSD) (49.1)

85

13

100

Hurricanes (H) (5.9)

9

2

11

Hurricane Days (HD) (24.5)

35

6

40

Intense Hurricanes (IH) (2.3)

5

1

6

Intense Hurricane Days (IHD)

11.75

1

13

Net Tropical Cyclone Activity (NTC) (100%)

183

30

215

 

3.                  U.S. Landfall Probability Forecast for October

 

We have recently developed a methodology for calculating the probability of hurricane landfall along the entire U.S. coastline for the month of October.  Based on a 1950-2001 dataset, we have calculated the probability of various intensity classes of tropical cyclones making landfall in October.  These forecast probabilities are based on our October NTC values.  For our forecast of an October 2005 NTC value of 30, our United States landfall probabilities are given in Table 6.  Landfall probabilities for the U.S. are above average for this October based on an above-average forecast of Atlantic basin NTC for October. 

 

Table 6:  Estimated probability (expressed in percent) of one or more U.S. landfalling tropical storms (TS), category 1-2 hurricanes (HUR) and category 3-4-5 hurricanes (IH) making landfall along the entire U.S. coast for October 2005 based on an October NTC forecast of 30.  The long-term mean October probability of one or more landfalling systems during the last 52 years is given in parentheses. 

 

Storm Category

October 2005 Probability

Named Storm (29%)

49%

Hurricane (15%)

21%

Intense Hurricane (6%)

15%

 

4          United States Major Hurricane Landfall Since 1995

 

The global climate signals since 1995 have been similar to the global climate signals of the mid-1920s to the mid-1960s when many more major hurricanes struck the U.S. East Coast and Florida.  Between 1995-2003, only 3 of 32 major Atlantic basin hurricanes (Cat. 3-4-5) made United States landfall (Opal (1995), Fran (1996), Bret (1999)).  Since August of last year, six of the eleven major hurricanes that formed in the Atlantic basin have made United States landfall (Charley (2004), Ivan (2004), Jeanne (2004), Dennis (2005), Katrina (2005) and Rita (2005)).  The long-term average is about one in three.  Even though the U.S. has experienced six major hurricane strikes since August 2004, in terms of the number of U.S. major hurricane strikes during the last 11 years (9 of 43 versus one of three for the century-long average) we have been, from this perspective, somewhat fortunate. 

 

5          Discussion

 

The 2005 hurricane season has been a very active one.  We expect total storm activity to reach near-record levels by the time the season ends on November 30.  June-July 2005 had the most early-season tropical cyclone activity on record (7 named storms, 2 hurricanes, 2 intense hurricanes and an NTC of 68).  August and September have also been quite active with the two months accruing an NTC of 115 (compared with the 51-year August-September average of 75).   Several factors were responsible for the very active Atlantic season this year.  Among these are:

 

1)      Warmer Atlantic sea surface temperatures (SST)

 

2)      Lower Atlantic sea level pressures (SLP)

 

3)      Lower vertical wind shear

 

4)      Moister lower and middle atmosphere

 

As was the case during the 2004 hurricane season, there has tended to be an anomalous ridge along the East Coast of the United States during the 2005 hurricane season.  This ridge has steered storms westward across the United States coastline instead of allowing them to recurve.  Figure 3 displays the anomalous 500 mb (~5.5 km altitude) ridge conditions that have been present during the July-September period of the 2005 season.  The high pressure over the northeast United States caused many of the western Atlantic and Caribbean-forming systems to be advected westward towards Mexico or the Gulf states.  The general character of the 2005 season has been different from that of 2004.  This year, the number of tropical cyclones which formed in the western part of the Atlantic basin has been much larger than last year.  Many more tropical cyclones formed in the central Atlantic last year. 

 

6          United States Landfalling Hurricane Webpage Application

 

Over the past four years, we have been compiling and synthesizing our landfalling hurricane data and have developed a webpage with extensive landfall probabilities for the Gulf and East Coasts of the United States.  In partnership with the GeoGraphics Laboratory at Bridgewater State College, a web application has been created that displays landfall probabilities for 11 regions, 55 subregions and all 205 U.S. coastal and near-coastal counties from Brownsville, Texas to Eastport, Maine.  Individual probabilities of sustained winds of tropical storm force (40-75 mph), hurricane force (≥ 75mph) and intense or major hurricane force (≥ 115 mph) are also given.  These probabilities are based on the current forecast of NTC and on current values of SSTA*.  Probabilities of winds in the vicinity of a subregion and county as well as 50-year probabilities for winds of tropical storm force, hurricane force and intense or major hurricane force are also provided.  These probabilities have recently been updated with data from the latter part of the 19th century with the release of the first part of the HURDAT reanalysis (Landsea et al. 2005).   Table 7 summarizes the data currently available on the webpage. 

 

Figure 3:  July-September 2005 500 mb (~5.5 km) geopotential height anomaly.  The high anomalies indicate ridge conditions which tend to steer tropical cyclones westward across the longitudes of the United States. 

 

 

Table 7: Data currently available on the CSU landfalling hurricane probability webpage.

 

 

Storm Category

Annual Landfall Probability

Annual Vicinity Probability

 

50-Year Probability

NS

X

X

X

H

X

X

X

IH

X

X

X

 

Figures 4 and 5 display example screens of data that are available on this website.  The user can select tracks of all intense hurricanes that have made landfall in a given area over the last 100 years.  This webpage is currently available at http://www.e-transit.org/hurricane.  One can also reach this webpage from a link off the CSU tropical meteorology project: http://hurricane.atmos.colostate.edu.


 

Figure 4: View of landfalling hurricane webpage centered on Subregion 1E – the Houston/Galveston metropolitan area. 

 

 

Figure 5: Example of data available from the United States landfalling hurricane webpage. 


7          The 1995-2005 Upswing in Atlantic Major Hurricanes and Global Warming

 

This year’s major hurricanes Dennis, Katrina and Rita and last year's four U.S. landfalling major hurricanes have spawned an abundance of questions concerning the role that global warming might be playing in these events.  The ideas that global warming may have been partly responsible for the last two years of greater landfalling hurricane activity has been enhanced by two recent papers presenting data to show that global tropical cyclones have become more intense in recent years.  They speculate that this increased hurricane activity may be due to human-induced global warming.  These papers are: 

 

a) Kerry Emanuel, 4 August 2005:  Increasing destructiveness of tropical cyclones over the past 30 years.  Nature, 436, 686-688.

 

b) P.J. Webster, G.J. Holland, J. Currie and P. Chang, 16 September 2005:  Changes in tropical cyclone number, duration, and intensity in a warming environment.  Science, 309, 1844-1846.

 

The first author’s comments concerning some of the flaws in the data sets that these papers used will be sent to the respective journals and will be put in the 2005 seasonal verification paper in a summarized form.

 

These papers’ implications that a Power Dissipation Index (PDI) (related to tropical cyclone intensity) has increased markedly in the Northwest Pacific and Atlantic over the last 30 years (Emanuel) and that global Category 4-5 tropical cyclone activity has gone up over the last 15 years (Webster et al.) from the prior 15 years are likely not valid.  Several factors need to be considered when evaluating these papers:

 

1)      The SSTs of the ocean basins where TCs form have warmed very little in the last 30 years (~0.2-0.3oC).  This warming is less than the 30 year warming of the whole globe.  Ocean temperature change has been matched by upper tropospheric warming.  Lapse rates and rainfall in the various tropical cyclone basins have shown no significant change.  We have no theory to relate TC basin SST variation to hurricane frequency and intensity when SST variations are so small.

 

2)      The Atlantic has special multi-decadal variations in major hurricane activity that are not present in other basins.  These changes are not related to global temperature but to multi-decadal variations of the Atlantic thermohaline circulation, sometimes referred to as the Atlantic multidecadal oscillation (AMO).  For example, there was naturally-occurring low major hurricane activity in the Atlantic from 1970-1994 and high major hurricane activity in the Atlantic from 1995-present. 

 

3)      There are special difficulties in using the NW Pacific data sets during the years of 1973-1986 when the Atkinson-Holliday (1977) wind pressure scheme was employed.  This is now well-accepted to have given typhoon maximum wind speeds that were much too low.  Much of the increase in a hurricane’s maximum winds from this period to the present is not real but due to erroneous wind under-estimates during the earlier period.   

 

4)      Major (Cat. 3-4-5) hurricane activity in the Northeast Pacific has gone down during the last two 15-year periods from 80 (1975-1989) to 74 (1990-2004), but the Webster et al. paper shows an increase in Category 4-5 tropical cyclones from 36 to 49.  This requires that Category 3 tropical cyclones decreased from 44 during 1975-1989 to 25 during 1990-2004.  This is highly unlikely.  SSTs in the NE Pacific increased by only 0.1oC between these two periods.

 

5)      Satellite technology and user training experience in the Southern Hemisphere in the period of 1975-1989 was not adequate to be able to make the fine distinction between a Category 4-5 hurricane and a Category 3 hurricane or the distinction of a storm with sustained surface winds above or below 130 mph.  The Webster et al. paper states that Southern Hemisphere Category 4-5 hurricanes increased from 33 to 72 from 1975-1989 to 1990-2004.  This requires that Category 3 hurricane increased from only 42 to 48 during the same period.  This is not physically plausible.  It is also not physically possible that Southern Hemisphere major (Cat. 3-4-5) hurricanes nearly doubled from 75 to 130 from 1975-1989 to 1990-2004.  Physical features present during the last 15 years were not that different from the prior 15 years. 

 

SUMMARY

 

We believe that there is likely little or no relationship between the small observed warming of the globe over the past thirty years and changes in global tropical cyclone activity or intensity. 

 

8          Forecast Theory and Cautionary Note

 

Our forecasts are based on the premise that those global oceanic and atmospheric conditions which preceded comparatively active or inactive hurricane seasons in the past provide meaningful information about similar trends in future seasons.  It is important that the reader appreciate that these seasonal forecasts are based on statistical schemes, which, owing to their intrinsically probabilistic nature, will fail in some years.  Moreover, these forecasts do not specifically predict where within the Atlantic basin these storms will strike.  The probability of landfall for any one location along the coast is very low and reflects the fact that, in any one season, most U.S. coastal areas will not feel the effects of a hurricane no matter how active the individual season is.  However, it must also be emphasized that a low landfall probability does not insure that hurricanes will not come ashore. 

 

9          Forthcoming 2005 Hurricane Activity Verification and Upcoming Forecasts

 

We will be issuing our forecast verification for the 2005 Atlantic basin hurricane season on Friday, November 18.  The first forecast for the 2006 hurricane season will be issued on Tuesday, December 6.  All forecasts are available on our website at: http://hurricane.atmos.colostate.edu/Forecasts.

 

10        Acknowledgments

 

Besides the individuals named on page 2, there have been a number of other meteorologists that have furnished us with data and given valuable assessments of the current state of global atmospheric and oceanic conditions.  These include Arthur Douglas, Richard Larsen, Todd Kimberlain, Ray Zehr, and Mark DeMaria.  In addition, Barbara Brumit and Amie Hedstrom have provided excellent manuscript, graphical and data analysis and assistance over a number of years.  We have profited over the years from many in-depth discussions with most of the current and past NHC hurricane forecasters.  The first author would further like to acknowledge the encouragement he has received for this type of forecasting research application from Neil Frank, Robert Sheets, Robert Burpee, Jerry Jarrell, former directors of the National Hurricane Center (NHC), and from the current director, Max Mayfield and their forecast staffs.  Uma Shama and Larry Harman of Bridgewater State College, MA have provided assistance and technical support in the development of our Landfalling Hurricane Probability Webpage.  We also thank Bill Bailey of the Insurance Information Institute for his sage advice and encouragement.

 

The financial backing for the issuing and verification of these forecasts has in part been supported by the National Science Foundation and by the Research Foundation of Lexington Insurance Company (a member of the American International Group).  We also thank the GeoGraphics Laboratory at Bridgewater State College for their assistance in developing the Landfalling Hurricane Probability Webpage.

 

11        Citations and Additional Reading


12        Verification of Previous Forecasts

 

Table 8:  Summary verification of the authors’ six previous years of seasonal forecasts for Atlantic TC activity between 1999-2004.  Verification of our earlier year forecasts for the years 1984-1998 are given in our late November seasonal verifications (on this web location). 

 

 

1999

 

5 Dec. 1998

Update

7 April

Update

4 June

Update

6 August

 

Obs.

No. of Hurricanes

9

9

9

9

8

No. of Named Storms

14

14

14

14

12

No. of Hurricane Days

40

40

40

40

43

No. of Named Storm Days

65

65

75

75

77

Hurr. Destruction Potential

130

130

130

130

143

Intense Hurricanes

4

4

4

4

5

Intense Hurricane Days

10

10

10

10

15

Net Tropical Cyclone Activity

160

160

160

160

193

 

 

2000

 

8 Dec. 1999

Update

7 April

Update

7 June

Update

4 August

 

Obs.

No. of Hurricanes

7

7

8

7

8

No. of Named Storms

11

11

12

11

14

No. of Hurricane Days

25

25

35

30

32

No. of Named Storm Days

55

55

65

55

66

Hurr. Destruction Potential

85

85

100

90

85

Intense Hurricanes

3

3

4

3

3

Intense Hurricane Days

6

6

8

6

5.25

Net Tropical Cyclone Activity

125

125

160

130

134

 

 

2001

 

7 Dec. 2000

Update

6 April

Update

7 June

Update

7 August

 

Obs.

No. of Hurricanes

5

6

7

7

9

No. of Named Storms

9

10

12

12

15

No. of Hurricane Days

20

25

30

30

27

No. of Named Storm Days

45

50

60

60

63

Hurr. Destruction Potential

65

65

75

75

71

Intense Hurricanes

2

2

3

3

4

Intense Hurricane Days

4

4

5

5

5

Net Tropical Cyclone Activity

90

100

120

120

142

 

 

2002

 

7 Dec. 2001

Update

5 April

Update

31 May

Update

7 August

Update

2 Sept.

 

Obs.

No. of Hurricanes

8

7

6

4

3

4

No. of Named Storms

13

12

11

9

8

12

No. of Hurricane Days

35

30

25

12

10

11

No. of Named Storm Days

70

65

55

35

25

54

Hurr. Destruction Potential

90

85

75

35

25

31

Intense Hurricanes

4

3

2

1

1

2

Intense Hurricane Days

7

6

5

2

2

2.5

Net Tropical Cyclone Activity

140

125

100

60

45

80

 

 

2003

 

6 Dec. 2002

Update

4 April

Update

30 May

Update

6 August

Update

3 Sept.

Update

2 Oct.

 

Obs.

No. of Hurricanes

8

8

8

8

7

8

7

No. of Named Storms

12

12

14

14

14

14

14

No. of Hurricane Days

35

35

35

25

25

35

32

No. of Named Storm Days

65

65

70

60

55

70

71

Hurr. Destruction Potential

100

100

100

80

80

125

129

Intense Hurricanes

3

3

3

3

3

2

3

Intense Hurricane Days

8

8

8

5

9

15

17

Net Tropical Cyclone Activity

140

140

145

120

130

155

173

 

 

2004

 

5 Dec. 2003

Update

2 April

Update

28 May

Update

6 August

Update

3 Sept.

Update

1 Oct.

 

Obs.

No. of Hurricanes

7

8

8

7

8

9

9

No. of Named Storms

13

14

14

13

16

15

14

No. of Hurricane Days

30

35

35

30

40

52

46

No. of Named Storm Days

55

60

60

55

70

96

90

Intense Hurricanes

3

3

3

3

5

6

6

Intense Hurricane Days

6

8

8

6

15

23

22

Net Tropical Cyclone Activity

125

145

145

125

185

240

229