This post presents the annual cycle in sea surface temperatures for the hurricane main development region in the North Atlantic. It also presents the sea surface temperature anomalies for three regions: (1) the Main Development Region, (2) the Gulf of Mexico and (3) the Coastal Waters north of the tropics along the East Coast of the United States, which is the extratropical portion of Hurricane Sandy’s path. Those three subsets are presented in weekly and monthly formats using the satellite-based Reynolds OI.v2 sea surface temperature dataset, and I’ve also shown them based on NOAA’s ERSST.v3b long-term sea surface temperature reconstruction. And since tropical storm development is inhibited by El Niño events, I’ve also presented the weekly NINO3.4 sea surface temperature anomalies. As an afterthought, I’ve added the weekly data for the Caribbean.
The 2013 hurricane season is fast approaching. Last month, Klotzbach and Gray of Colorado State University published their Extended Range Forecast of Atlantic Seasonal Hurricane Activity and Landfall Strike Probability for 2013. The opening page reads:
We anticipate that the 2013 Atlantic basin hurricane season will have enhanced activity compared with the 1981-2010 climatology. The tropical Atlantic has anomalously warmed over the past several months, and it appears that the chances of an El Niño event this summer and fall are unlikely. We anticipate an above-average probability for major hurricanes making landfall along the United States coastline and in the Caribbean. 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 or how little activity is predicted.
Figure 1 – Annual Cycle in Main Development Region Sea Surface Temperatures
Sea surface temperatures are an important component of hurricane development. Tropical storms need a lot of warm water to grow. The following is a paragraph from Chapter 4.18 [ENSO Influence on Tropical Cyclones (Hurricanes)] from my book Who Turned on the Heat?
The recipe for a tropical cyclone has three primary ingredients. The first is warm water—waters in excess of 26 deg C. Because the tropical storm feeds off the warm water, it cools the sea surface, so the warm water has to reach depths of about 60 meters in order to support the development of the tropical cyclone. The second ingredient is moisture and lots of it. The moisture has to cover a large area and be thick, normally extending from the sea surface to altitudes to 20,000 feet (about 465mb). The third ingredient is relatively light winds. That’s where an El Niño spoils the recipe.
An El Niño event in the tropical Pacific causes stronger-than-normal high level westerly winds in the Main Development Region of the tropical North Atlantic, and those strong high level winds can cause wind shear.
Figure 1 shows the annual cycle in sea surface temperatures for the Main Development Region in the North Atlantic, which is bordered by the coordinates of 10N-20N, 80W-20W. It’s easy to see why the official Atlantic hurricane season lasts from June through November. Sea surface temperatures in the Main Development Region are coolest in February and March and warmest in September and October.
So where do we sit this year? And what about the Gulf of Mexico? And the waters off the east coast of the U.S. where Sandy tracked last year before making the left turn into New Jersey?
WEEKLY SEA SURFACE TEMPERATURE ANOMALIES
Weekly sea surface temperature and temperature anomaly data (deviations from the average monthly values of the period of 1971-2000) based on the Reynolds OI.v2 dataset are available from NOAA NOMADS website—as are the short-term (November 1981 to present) monthly data that follow. The Reynolds OI.v2 dataset is based on satellite data and from ship inlets and buoys (fixed and floating). The weekly data is centered on Wednesdays and begins in January 1990.
Figure 2 shows the weekly sea surface temperature anomalies for the main development region through Wednesday May 8, 2013. I’ve also highlighted the current value in red as the horizontal line. Klotzbach and Gray were obviously correct with, “The tropical Atlantic has anomalously warmed over the past several months…”
Those living along the Gulf Coast are always concerned about the sea surface temperature anomalies in the Gulf of Mexico. At present, sea surface temperature anomalies there are below the 1971-2000 average by a significant amount. See Figure 3. That’s not to say that the Gulf won’t spawn any hurricanes this year. This is simply an indication that sea surface temperatures in the Gulf, as a whole, are cooler than normal now.
And those living along the Eastern Seaboard are concerned about the sea surface temperatures along the East Coast. I’ve used the same coordinates in Figure 4 that I used for the discussions of sea surface temperatures along the extratropical portion of Sandy’s storm track in two posts last year. See here and here. At present, sea surface temperature anomalies are below the average of the base period of 1971 to 2000.
And, yes, that severe drop toward the end of 2012 occurred the week of Sandy. While sea surface temperatures were not exceptionally warm last year along the extratropical storm track, Sandy did pull a lot of heat from that portion of the Atlantic. I’ll let you decide if that will impact the storms this year.
SATELLITE-ERA MONTHLY DATA
For those interested in a longer-term look at the data, Figures 5, 6 and 7 present the monthly sea surface temperature anomalies for those regions, again using the Reynolds OI.v2 dataset. The monthly data starts in November 1981 and runs through April 2012. I’ve also included the most recent values as red horizontal lines for easier comparisons.
MONTHLY LONG-TERM RECONSTRUCTION
And for those wanting a further look back in time, Figures 8 through 10 show the April 2012 sea surface temperatures highlighted in red for the 3 regions, using NOAA’s ERSST.v3b dataset, which starts in January 1854. The ERSST.v3b data is available through the KNMI Climate Explorer. Due to the number of corrections before 1950 and the severity of them, the early data has to be looked on with a pinch of salt, especially when looking at relatively small regions as we are with Figures 9 and 10.
What I did find surprising, Figure 11, was that the main development region data remained relatively flat from 1930 to 1995. That is, according to the ERSST.v3b data, there was little warming there for 6 ½ decades. In Figure 11, the red line is the linear trend as determined by EXCEL.
EL NIÑO-SOUTHERN OSCILLATION
As noted earlier, El Niño events in the tropical Pacific cause increased wind shear in the North Atlantic and that suppresses hurricane development there. The ENSO forecasting models are not predicting an El Niño event this season, see pages 25 through 27 of NOAA’s weekly ENSO update, so Klotzbach and Gray considered the absence of El Niño conditions when making their hurricane season predictions.
Figure 12 presents a graph of the weekly sea surface temperature anomalies for the NINO3.4 region in the east-central equatorial Pacific. NINO3.4 sea surface temperature anomalies are a commonly used index of the strength, frequency and duration of El Niño and La Niña events. According to NOAA, El Niño conditions exist when the sea surface temperature anomalies are warmer than +0.5 deg C. As of last week, the NINO3.4 data was showing an anomaly of effectively zero.
OOPS FORGOT TO ISOLATE THE CARIBBEAN
The Main Development Region is quite large, extending from the Caribbean Sea to almost the coast of Africa, and sea surface temperatures can differ quite a bit from west to east. Figure 13 shows the weekly sea surface temperature anomalies for the Caribbean Sea, using the coordinates of 10N-20N, 84W-60W. Sea surface temperatures there are also above normal, but not as high as they are toward the eastern portion of the main development region.
For four years, I’ve been illustrating and discussing how ocean heat content and satellite-era sea surface temperature data indicate the oceans warmed naturally. That doesn’t stop climate change alarmists from making all sorts of nonsensical claims. If the natural warming of the oceans is new to you, refer to the illustrated essay “The Manmade Global Warming Challenge” [42MB].
Figure 14 is a sea surface temperature anomaly map of the North Atlantic, for the week centered on May 8, 2013. Just because sea surface temperature anomalies are below normal along the Gulf and southeast coasts right now, that doesn’t mean they’re going to remain there for the 2013 hurricane season. Also, hurricanes don’t care about anomalies. Sea surface temperatures can be below normal, but if they’re warm enough (in absolute terms), they’ll support a hurricane.
As Roger Pielke, Jr. reminded us last December in his post Record US Intense Hurricane Drought Continues:
When the Atlantic hurricane season starts next June 1, it will have been 2,777 days since the last time an intense (that is a Category 3, 4 or 5) hurricane made landfall along the US coast (Wilma in 2005). Such a prolonged period without an intense hurricane landfall has not been observed since 1900.
While this fact counters many claims by global warming enthusiasts, it also indicates we’re long overdue for one.