2015 Atlantic Hurricane Season

The CSU initial forecast for Atlantic basin tropical cyclone activity in 2015 has been released with the following lead-in comments: "We anticipate that the 2015 Atlantic basin hurricane season will be one of the least active seasons since the middle of the 20th century. It appears quite likely that an El NiÃ±o of at least moderate strength will develop this summer and fall. The tropical and subtropical Atlantic are also quite cool at present. We anticipate a below-average probability for major hurricanes making landfall along the United States coastline and in the Caribbean."

As of the end of February an El Nino is in place and it is expected to increase in strength with at least a moderate El Nino quite likely for the entire Atlantic hurricane season. Some of the forecast models including the suggest that a strong El Nino event will occur. Since the end of November, 2014, SSTs in almost all of the Atlantic tropical basin have declined considerably with anomalies greater than -1.5C in some areas in the eastern Atlantic and the western Caribbean Sea. This significant shift downward in tropical Atlantic SSTs will produce another year of decreased activity in the basin and it also reduces the likelihood of any early season storms. The CSU forecast numbers are 7 tropical storms, with 3 of them becoming hurricanes with one hurricane becoming a major storm. This is one of the lowest CSU tropical cyclone forecasts that I have ever seen them issue. They also expected an ACE of 40 and a seasonal activity level at 45% of normal.

CSU lists 1991 as one of their analog years, however, with such a rapid decline in the overall Atlantic tropical SSTs, I believe that 1969 and 1991 are no longer valid analogs. My new analog years are:

1. 1977 - Atlantic activity was 6/5/1 ....... EASTPAC activity was 8/4/0
2. 1959 - Atlantic activity was 10/6/2 ...... EASTPAC activity was 15/5/3
3. 1953 - Atlantic activity was 13/6/4 ...... EASTPAC activity was 4/2/0

The updated averages for these analog years is 10/6/2 - which is close to my current forecast of 9/6/2. (updated on 4/15 to 8/5/1)

TSR also issued its updated forecast for the Atlantic basin and lowered their forecast totals to 11/5/2 with the following comments: "The TSR forecast has been reduced, since early December 2014, due to updated climate signals indicating that the tropical North Atlantic and Caribbean Sea in August-September 2015 will likely be cooler than normal and cooler than thought previously. Should the TSR forecast for 2015 verify it would mean that the ACE index total for 2013-2015 was easily the lowest 3-year total since 1992-1994 and it would imply that the active phase of Atlantic hurricane activity which began in 1995 has likely ended. However, it should be stressed that the precision of hurricane outlooks issued in April is low and that large uncertainties remain for the 2015 hurricane season."

As the season gets underway, keep an eye on the level of activity in the EASTPAC. If it starts to look like the Eastern Pacific is going to have a busy year, then 1953 can be discarded as an analog year for the Atlantic - which means that the upcoming Atlantic hurricane season could be mighty quiet - especially if the tropical Atlantic SST cooling trend continues into the Summer.

Remember that you can post your own forecast of seasonal numbers in the Storm Forum until the season starts on June 1st.
ED

Edited by Ed Dunham (Wed Apr 15 2015 05:43 PM)

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