Klotzbach and Gray 2012 forecast – cooler Atlantic – fewer hurricanes

EXTENDED RANGE FORECAST OF ATLANTIC SEASONAL HURRICANE ACTIVITY AND LANDFALL STRIKE PROBABILITY FOR 2012

We anticipate that the 2012 Atlantic basin hurricane season will have reduced activity compared with the 1981-2010 climatology. The tropical Atlantic has anomalously cooled over the past several months, and it appears that the chances of an El Niño event this summer and fall are relatively high. We anticipate a below-average probability for major hurricanes making landfall along the United States coastline and in the Caribbean. However, coastal residents are reminded that it only takes one hurricane making landfall to make it an active season for them, and they need to prepare the same for every season, regardless of how much activity is predicted.

ABSTRACT

Information obtained through March 2012 indicates that the 2012 Atlantic hurricane season will have less activity than the median 1981-2010 season. We estimate that 2012 will have about 4 hurricanes (median is 6.5), 10 named storms (median is 12.0), 40 named storm days (median is 60.1), 16 hurricane days (median is 21.3), 2 major (Category 3-4-5) hurricanes (median is 2.0) and 3 major hurricane days (median is 3.9). The probability of U.S. major hurricane landfall is estimated to be about 80 percent of the long-period average. We expect Atlantic basin Net Tropical Cyclone (NTC) activity in 2012 to be approximately 75 percent of the long-term average.

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 anticipate a somewhat below-average Atlantic basin hurricane season due to a combination of an anomalously cool tropical Atlantic and the potential development of El Niño. Coastal residents are reminded that it only takes one hurricane making landfall to make it an active season for them, and they need to prepare the same for every season, regardless of how much activity is predicted.

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Currently, SSTs are generally 0.0°C – 0.5°C below average across most of the eastern and central tropical Pacific, except for the extreme eastern part of the tropical Pacific where SSTs are above average. Table 7 displays January and March SST anomalies for several Nino regions. Note that the central and eastern tropical Pacific has experienced considerable warming since January.

Table 7: January and March SST anomalies for Nino 1+2, Nino 3, Nino 3.4, and Nino 4, respectively. March-January SST anomaly differences are also provided.

There is considerable uncertainty as to what is going to happen with the current weak La Niña event. The spring months are known for their ENSO predictability barrier. This is when both statistical and dynamical models show their least amount of skill. This is likely due to the fact that from a climatological perspective, trade winds across the Pacific are weakest during the late spring and early summer, and therefore, changes in phase of ENSO are often observed to occur during the April-June period. By August-October, several models are predicting El Niño conditions to develop, while the rest predict ENSO-neutral conditions (Figure 9). We find that, in general, the European Centre for Medium-Range Weather Forecasts (ECMWF) shows the best prediction skill of the various ENSO models.

The correlation skill between a 1 March forecast from the  ECMWF model system 3 and the observed September Nino 3.4 anomaly is 0.71, based on hindcasts/forecasts from 1982-2010, explaining half of the variance in Nino 3.4 SST. The ECMWF has recently upgraded to system 4, which is likely to have even better skill than the previous version. The hindcast skill from ECMWF is very impressive, considering that the prediction goes through the springtime predictability barrier. The average of the various ECMWF ensemble members is calling for a September Nino 3.4 SST anomaly of approximately 0.8°C, giving us increased confidence in our expectation for a weak El Niño by the peak of the hurricane season in September.

Approximately 2/3 of the ECMWF ensemble members are calling for SSTs to approach El Niño levels (anomaly >= 0.5°C) by September (Figure 10).

Figure 9: ENSO forecasts from various statistical and dynamical models. Figure courtesy of the International Research Institute (IRI). By August-October, several models are calling for El Niño conditions while the rest are calling for ENSO-neutral conditions to be present.

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ATLANTIC BASIN SEASONAL HURRICANE FORECAST FOR 2012

Forecast Parameter and 1981-2010

Median (in parentheses)

Issue Date

4 April 2012

Named Storms (NS) (12.0) 10

Named Storm Days (NSD) (60.1) 40

Hurricanes (H) (6.5) 4

Hurricane Days (HD) (21.3) 16

Major Hurricanes (MH) (2.0) 2

Major Hurricane Days (MHD) (3.9) 3

Accumulated Cyclone Energy (ACE) (92) 70

Net Tropical Cyclone Activity (NTC) (103%) 75

Full forecast here:

http://tropical.atmos.colostate.edu/forecasts/2012/apr2012/apr2012.pdf