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Tuesday, July 8, 2008

Hurricane Breeding Grounds

In this post, I’ll examine SST anomalies in the Tropical North Atlantic, the Caribbean Sea, and the Gulf of Mexico.


Figure 1 illustrates Tropical North Atlantic SST anomalies from January 1854 to May 2008. They vary little from North Atlantic SST anomalies for the same period. If anything, the Tropics are slightly dampened. Refer to Figure 2.

Figure 1

Figure 2

In Figure 3, the time span for the Tropical North Atlantic SST anomaly data was shortened to the last 30+ years. The stand-out features in the Tropical North Atlantic are the peaks in October 2003 and April 2005 and the significant drop in SST since April 2005, almost 0.5 deg C.
April 2005 = 0.855 deg C
May 2008 = 0.359 deg C
Difference = 0.496 deg C
Figure 3


The SST anomaly for the Caribbean Sea from January 1854 to May 2008 is shown in Figure 4. As illustrated in Figure 5, its curve is very similar to the North Atlantic SST anomaly, too.

Figure 4

Figure 5

Figure 6 illustrates the Caribbean Sea SST anomaly from January 1978 to May 2008. Its anomaly peaked in June 2005. Since then, SSTs have dropped more than 1 deg C.
June 2005 = 1.082 deg C
May 2008 = 0.053 deg C
Difference = 1.029 deg C
Figure 6


The peak SST anomaly of the Gulf of Mexico occurred in 1938, as illustrated in Figure 7, which shows Gulf of Mexico SST anomalies from January 1854 to May 2008. Like all the other long-term anomaly graphs, Figure 7 has been smoothed with an 85-month running-average filter. Figure 8 provides a comparison to North Atlantic SST anomaly. The Gulf of Mexico SST mimics North Atlantic SST until the early 1980s, when it diverges from then lags the North Atlantic.

Figure 7

Figure 8

The month-to-month Gulf of Mexico SST signal is so volatile it had to be smoothed with a 12-month filter to determine any underlying trend since January 1978. Refer to Figures 9 and 10. Between 1978 and 1998, there was a flat to slightly downward trend in the Gulf. Then there’s the step change in 1998 and an upward trend that follows.
Figure 9

Figure 10


Sea Surface Temperature Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).


Anonymous said...

Are the data that went into the jpgs available?

Also what are the boundaries for the northern tropical Atlantic, Gulf, and Caribbean?


Bob Tisdale said...

jweisham: The coordinates I used for the datasets were:
Tropical North Atlantic: 0-24N, 82W-12E
Gulf of Mexico: 16N-20N, 98W-82W
Caribbean: 10N-20N, 85W-60W

The instructions for downloading the data are here:

The starting point in the instructions would be here:

It’s pretty straightforward. Give me a holler back if you’ve got questions or run into a problem.



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