The peak of the Atlantic Hurricane season is rapidly approaching. See the NOAA Hurricane Climatology graph to the right. (Give it a click for a full-sized version.) Hurricane frequency tends to peak in mid-September.
In the May 2014 post Hurricane Development Region Sea Surface Temperature Anomalies as We Start the 2014 Season, we presented sea surface temperature anomalies for the Main Development Region (10N-20N, 80W-20W) and for the Gulf of Mexico (21N-31N, 98W-81W) in 3 formats: (1) monthly long-term (1854 to present), (2) monthly satellite-era (1981 to present) and (3) weekly satellite-era (1990 to present). In this post, we’ll only update the weekly data, and we’ll add the data for the Caribbean (10N-20N, 84W-60W) and the Extratropical Eastern Coastal Waters of the United States (24N-40N, 80W-70W). (A map showing where those regions are located is included as the final illustration.)
SEA SURFACE TEMPERATURE CLIMATOLOGIES FOR THE FOUR REGIONS
First, before we look at the anomaly data, I don’t believe I’ve ever presented how the sea surface temperatures for those regions normally vary throughout a year.
Figure 2 presents the average monthly sea surface temperatures, over the course of a year, for the base period of 1971 to 2000, which is the base period used by NOAA for its Reynolds OI.v2 dataset. In other words, they are the reference temperatures—the “normals”—from which anomalies are calculated. Sea surface temperatures (not anomalies) for the Main Development Region and the Caribbean normally peak in September and October. And the surface temperatures of the Gulf of Mexico and the Extratropical Eastern Coastal Waters of the United States normally peak in August.
I’ve included a red horizontal line at 26 deg C, which is considered the sea surface temperature needed for hurricane development. (I’ve also seen 26.5 deg C discussed.) Normally, the surface temperatures of the Main Development Region and the Gulf of Mexico reach that threshold about the beginning of May, while the Extratropical Eastern Coastal Waters don’t normally cross the threshold until June. Sea surface temperatures in the Caribbean are normally above the threshold year round. Obviously, there are factors other than warm water needed for hurricane development.
WEEKLY SEA SURFACE TEMPERATURE ANOMALIES
For the week centered on Wednesday, August 13, 2014, the surface temperature anomalies for the Caribbean (Figure 3) are slightly above the 1971-2000 “normals”.
Gulf of Mexico waters, on the other hand, are presently towards the high end of their recent range of variability. See Figure 4. In addition to variations caused by weather, the weekly sea surface temperature anomalies there appear to also have a strong seasonal component.
And as shown in Figure 5, the most recent weekly sea surface temperatures of the extratropical waters off the east coast of the U.S. are also above the 1971-2000 “normals”, but not exceptionally warm. Then again, as we discussed after Sandy strolled up those waters back in 2012, the sea surface temperatures in that region have cooled (not warmed) since the great New England hurricane of the 1930s. See the posts here and here.
Last but not least, Figure 6, the sea surface temperature anomalies for the Main Development Region are below (not above) the normals for 1971-2000.
IMPORTANT CLOSING NOTE
Current sea surface temperatures (absolute) are capable of spawning hurricanes…a result of the normal seasonal change in surface temperatures. See the map in Figure 7. And while the recent El Niño conditions in the Pacific tend to suppress hurricane development by effectively chopping the tops off the developing hurricanes (the result of wind shear in the tropical North Atlantic caused by the El Niño), hurricanes can still form and will likely continue do so this season.
The NOAA Reynolds OI.v2 sea surface temperature data and maps are available in absolute and anomaly forms through the NOAA NOMADS website
Thanks, Bob. A very informative article.
Colorado State University Forecast of Atlantic Hurricane Activity from August 14-August 27, 2014 (.pdf, 14 August 2014) [two-week forecast]:
We believe that the next two weeks will be characterized by activity at below-average levels (less than 70 percent of climatology). The average ACE accrued during the period from 1981-2010 for August 14-August 27 was 12 units, and consequently, our forecast for the next two weeks is for less than 9 ACE units to be generated.
Click to access august_14_2014.pdf
Thanks for the CSU forecast, Andres.
And now ….
Colorado State University Forecast of Atlantic Hurricane Activity from August 28-September 10, 2014
(.pdf, 28 August 2014) [two-week forecast]:
We believe that the next two weeks will be characterized by activity at below-average levels (less than 70 percent of climatology). The average ACE accrued during the period from 1981-2010 from August 28-September 10 was 24 units, and consequently, our forecast for the next two weeks is for 17 or fewer ACE units to be generated.
The below-average forecast is due to several factors. Hurricane Cristobal is estimated to generate 2-4 ACE units before undergoing extra-tropical transition in the next couple of days. Three areas are currently being watched for development in the next few days by the National Hurricane Center, but only one is given a moderate chance of development in the next five days. Long-range models do not indicate any other significant development chances in the 1-2 week timeframe.
Thanks, Bob, for keeping this blog.
I forgot to add the source:
Click to access august_28_2014.pdf