Top Forecasters Update The North Atlantic Tropical Cyclone Season Forecast

Strong Positive Phase Pacific North America/North Atlantic Oscillation Indices Bring Hot Risk
08/02/2021, 12:40 pm EDT
Support for La Nina Ahead Increasing Rapidly
08/09/2021, 7:53 am EDT
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All primary seasonal forecasts for the North Atlantic tropics are updated. The seasonal forecasts indicated include the activity observed so far. The Climate Impact Company added 1 major hurricane and increased the ACE index. However, both Colorado State University and Tropical Storm Risk U.K. lowered their forecast from previous and are each now very close to Climate Impact Company. The NOAA/NHC forecast increased.

Highlight: ALL seasonal forecasts are updated. Consensus shows seasonal activity lowered slightly but still more active than normal.

Discussion: All primary seasonal forecasts for the North Atlantic tropics are updated. The seasonal forecasts indicated include the activity observed so far (Table 1). The Climate Impact Company added 1 major hurricane and increased the ACE index. However, both Colorado State University and Tropical Storm Risk U.K. lowered their forecast from previous and are each now very close to Climate Impact Company. The NOAA/NHC forecast increased.

(Early June Forecast)Tropical StormsHurricanesIntense HurricanesACE

Index

Climate Impact Company16

(16)

8

(8)

4

(3)

134

(106)

Colorado State University18

(20)

8

(9)

4

(4)

150

(160)

Tropical Storm Risk, U.K.18

(20)

7

(9)

3

(4)

122

(141)

NOAA/

NHC

 

15-21

(13-20)

7-10

(6-10)

3-5

(3-5)

N/A
2021 Season So Far

 

51011

 Table 1: Early August North Atlantic tropical cyclone seasonal activity forecasts are updated.

Climate diagnostics continue to support a very active season. However, the delay in start to the busiest time of year causes CSU and TSR to cut back their forecast slightly to the CIC values. La Nina is forecast to develop although not as strong as last year. La Nina is very supportive of a busy tropical cyclone year. The North Atlantic tropics/subtropics are trending slightly warmer but remain mostly near normal and cooler than last year and the 20-year climatology. Some warming the tropical basin is expected during AUG/SEP/OCT.

The location and strength of the Bermuda high-pressure system is likely to guide systems developing in the central tropics toward the Gulf of Mexico or Southeast/Mid-Atlantic States most prominently in September. Systems forming in the outer tropics may have a tendency to turn northwest quickly.