CFSv2-based Dynamical–Statistical Forecast for the 2019 Atlantic Hurricane Season: July Update

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CFSv2-based Dynamical–Statistical Forecast for the 2019 Atlantic Hurricane Season:

July Update

CFSv2 ICs: 6–20 July 2019

Hui Wang

Climate Prediction Center NOAA/NWS/NCEP

July 21, 2019

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Background

• Prediction methodology

• Hurricane climatology (entire season)

• Definitions of above-, near-, & below-normal seasons

Forecasts

• ASO SST and wind shear anomaly (CFSv2 ensemble forecast)

• Hurricane season forecast for the Atlantic basin (July update)

• Forecast range is determined by forecast  one standard deviation of inter-member spreads.

• Probability forecast is based on 60 members of CFSv2 forecasts and NOAA’s definitions of below-, near- and above-normal criteria.

Verification of Past Forecasts

• 2008–2018

• Atlantic basin

• Forecast skills:

Anomaly correlation (AC) Hit rate

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Prediction Methodology

 Regression period: 1982–2018

 2 predictors: CFS ASO MDR U200–U850 Observed preseason (Apr–Jun) NATL SST

 Regions used to construct predictors MDR: 20ôW – 80ôW, 10ôN – 20ôN

(Main development region for wind shear) NATL: 30ôW – 60ôW, 55ôN – 65ôN

(North Atlantic for SST)

Atlantic Seasonal Hurricane Activity

Reference:

Wang, H., J. K. Schemm, A. Kumar, W. Wang, L. Long, M. Chelliah, G. D. Bell, and P. Peng, 2009: A statistical forecast model for Atlantic seasonal hurricane activity based on the NCEP dynamical seasonal forecast. J. Climate, 22, 4481–4500.

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Atlantic

Period 1982 – 2018 1982 – 1994 1995 – 2018

Named Storms

12.2 8.5 14.3

Hurricanes

6.5 4.5 7.5

Major Hurricanes

2.7 1.3 3.5

ACE

106.5 60.3 131.5

Climatology

Entire Hurricane Season

Definitions of Above-, Near-, and Below-Normal Seasons

ATLANTIC

Season Type Range of

Named Storms Range of

Hurricanes Range of Major

Hurricanes Range of ACE

Above-Normal

≥ 13 ≥ 7 ≥ 3 ≥ 120%

Near-Normal

9–12 5–6 2 71.4–120%

Below-Normal

≤ 8 ≤ 4 ≤ 1 ≤ 71.4%

ACE median: 92.5

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MDR

April ICs

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MDR

July ICs

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MDR

April ICs

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July ICs

MDR

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April ICs

MDR

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July ICs

MDR

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CFSv2 ICs

04/13 – 04/27/2019^{April ICs:}

July ICs:

07/06 – 07/20/2019

Named Storms Range

Probability

10 8 – 12

25% 60% 15%

15 13 – 16 0% 4% 96%

Hurricanes Range Probability

5 4 – 6

35% 47% 18%

8 7 – 9

0% 5% 95%

Major Hurricanes

Range Probability

2 2 – 3

18% 56% 26%

4 3 – 4

0% 0% 100%

ACE Range Probability

86%

57% – 114%

35% 52% 13%

153%

129% – 177%

0% 10% 90%

Below Near Above Normal

Below, Near & Above Normal Below Near Above

Below Near Above Below Near Above

Forecasts for the Atlantic Basin

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AC: Anomaly correlation skill Hit: Hit rate when OBS falls into the forecast range.

OBS Fore

cast

Light blue shading: Forecast range determined by ± one standard deviation of the spreads of 60 members.

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AC: Anomaly correlation skill Hit: Hit rate when OBS falls into the forecast range.

OBS Fore

cast

Light blue shading: Forecast range determined by ± one standard deviation of the spreads of 60 members.