2011 Atlantic Hurricane Predictions From Dr. William Gray

Wed Apr 13 16:47:19 PDT 2011

Below is the latest 2011 Atlantic hurricane season forecast from Dr. William
Gray of Colorado State University. Dr. Gray will update his forecast in June
. 

ATLANTIC BASIN SEASONAL HURRICANE FORECAST FOR 2011 Forecast Parameter and
1950-2000 

Climatology (in parentheses) 

Issue Date 

8 December 2010 

Issue Date 

6 April 2011 

Named Storms (NS) (9.6) 

17 

16 

Named Storm Days (NSD) (49.1) 

85 

80 

Hurricanes (H) (5.9) 

9 

9 

Hurricane Days (HD) (24.5) 

40 

35 

Major Hurricanes (MH) (2.3) 

5 

5 

Major Hurricane Days (MHD) (5.0) 

10 

10 

Accumulated Cyclone Energy (ACE) (96.1) 

165 

160 

Net Tropical Cyclone Activity (NTC) (100%) 

180 

175 

PROBABILITIES FOR AT LEAST ONE MAJOR (CATEGORY 3-4-5) HURRICANE LANDFALL ON
EACH OF THE FOLLOWING COASTAL AREAS: 

1) Entire U.S. coastline - 72% (average for last century is 52%) 

2) U.S. East Coast Including Peninsula Florida - 48% (average for last
century is 31%) 

3) Gulf Coast from the Florida Panhandle westward to Brownsville - 47%
(average for last century is 30%) 

PROBABILITY FOR AT LEAST ONE MAJOR (CATEGORY 3-4-5) HURRICANE TRACKING INTO
THE CARIBBEAN (10-20°N, 60-88°W) 

1)      61% (average for last century is 42%)

ABSTRACT 

Information obtained through March 2011 indicates that the 2011 Atlantic
hurricane season will have significantly more activity than the average
1950-2000 season. We estimate that 2011 will have about 9 hurricanes
(average is 5.9), 16 named storms (average is 9.6), 80 named storm days
(average is 49.1), 35 hurricane days (average is 24.5), 5 major (Category
3-4-5) hurricanes (average is 2.3) and 10 major hurricane days (average is
5.0). The probability of U.S. major hurricane landfall is estimated to be
about 140 percent of the long-period average. We expect Atlantic basin Net
Tropical Cyclone (NTC) activity in 2011 to be approximately 175 percent of
the long-term average. We have decreased our seasonal forecast slightly from
early December, due to anomalous warming in the eastern and central tropical
Pacific and cooling in the tropical Atlantic. 

This forecast is based on a new extended-range early April statistical
prediction scheme that utilizes 29 years of past data. Analog predictors are
also utilized. We expect current La Niña conditions to transition to
near-neutral conditions during the heart of the hurricane season. Overall,
conditions remain conducive for a very active hurricane season.

Table 1: Observed versus early April cross-validated hindcast NTC for
1982-2010 using our new forecast scheme. Average errors for cross-validated
hindcast NTC and climatological NTC predictions are given without respect to
sign. Red bold-faced years in the “Hindcast NTC” column are years that we
did not go the right way, while red bold-faced years in the “Hindcast
improvement over Climatology” column are years that we did not beat
climatology. The hindcast went the right way with regards to an above- or
below-average season in 21 out of 29 years (72%), while hindcast improvement
over climatology occurred in 19 out of 29 years (66%). The hindcast has
improved upon climatology in all but four years since 1993.

Year 

Observed NTC 

Hindcast NTC 

Observed minus 

Hindcast 

Observed minus Climatology 

Hindcast improvement over Climatology 

1982 

38 

101 

-63 

-62 

-1 

1983 

31 

20 

11 

-69 

58 

1984 

80 

163 

-82 

-20 

-63 

1985 

106 

60 

45 

6 

-40 

1986 

37 

32 

5 

-63 

58 

1987 

46 

71 

-25 

-54 

29 

1988 

117 

134 

-17 

17 

0 

1989 

130 

96 

34 

30 

-4 

1990 

100 

91 

9 

0 

-9 

1991 

58 

97 

-39 

-42 

3 

1992 

67 

20 

47 

-33 

-14 

1993 

52 

60 

-8 

-48 

40 

1994 

35 

71 

-35 

-65 

29 

1995 

222 

158 

64 

122 

58 

1996 

192 

189 

3 

92 

89 

1997 

54 

91 

-38 

-46 

9 

1998 

169 

166 

3 

69 

66 

1999 

182 

121 

60 

82 

21 

2000 

134 

154 

-21 

34 

13 

2001 

135 

113 

22 

35 

13 

2002 

83 

136 

-53 

-17 

-36 

2003 

175 

139 

36 

75 

39 

2004 

232 

89 

142 

132 

-11 

2005 

279 

185 

94 

179 

85 

2006 

85 

139 

-54 

-15 

-39 

2007 

99 

135 

-36 

-1 

-35 

2008 

162 

201 

-39 

62 

24 

2009 

69 

78 

-9 

-31 

22 

2010 

195 

235 

-40 

95 

55 

Average 

116 

116 

39 

55 

+16 

Current Atlantic Basin Conditions 

Conditions in the Atlantic are favorable for an active season. SSTs across
the tropical Atlantic remain at above-average levels (Figure 12). However,
these anomalies have cooled somewhat over the past several months, likely
due to a mid-winter switch from a negative phase of the North Atlantic
Oscillation (NAO) to a positive phase of the NAO (Figure 13). A positive
phase of the NAO is associated with anomalously strong trades across the
tropical Atlantic, which promotes enhanced mixing and upwelling resulting in
anomalous cooling. Figure 14 displays the cooling in SSTs observed in the
tropical Atlantic from the latter part of March minus the latter part of
January. The anomalous cooling has been on the wane over the past couple of
weeks as the NAO has migrated back towards a neutral state. The atmospheric
state across the tropical Atlantic looks quite favorable for an active
season, as wind shear anomalies across the basin have been well below
average over the past two months.

8 Landfall Probabilities for 2011 

A significant focus of our recent research involves efforts to develop
forecasts of the probability of hurricane landfall along the U.S. coastline
and in the Caribbean. Whereas individual hurricane landfall events cannot be
accurately forecast months in advance, the total seasonal probability of
landfall can be forecast with statistical skill. With the observation that
landfall is a function of varying climate conditions, a probability
specification has been developed through statistical analyses of all U.S.
hurricane and named storm landfall events during the 20th century
(1900-1999). Specific landfall probabilities can be given for all tropical
cyclone intensity classes for a set of distinct U.S. coastal regions. 

Net landfall probability is shown linked to the overall Atlantic basin Net
Tropical Cyclone activity (NTC; see Table 8). NTC is a combined measure of
the year-to-year mean of six indices of hurricane activity, each expressed
as a percentage difference from the long-term average. Long-term statistics
show that, on average, the more active the overall Atlantic basin hurricane
season is, the greater the probability of U.S. hurricane landfall. 

Table 8: NTC activity in any year consists of the seasonal total of the
following six parameters expressed in terms of their long-term averages. A
season with 10 NS, 50 NSD, 6 H, 25 HD, 3 MH, and 5 MHD would then be the sum
of the following ratios: 10/9.6 = 104, 50/49.1 = 102, 6/5.9 = 102, 25/24.5 =
102, 3/2.3 = 130, 5/5.0 = 100, divided by six, yielding an NTC of 107.
1950-2000 Average 

1) 

Named Storms (NS) 

9.6 

2) 

Named Storm Days (NSD) 

49.1 

3) 

Hurricanes (H) 

5.9 

4) 

Hurricane Days (HD) 

24.5 

5) 

Major Hurricanes (MH) 

2.3 

6) 

Major Hurricane Days (MHD) 

5.0 

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