Analyzing Apparent Temperature Trends in the U.S. Fifth Fleet Operating Area

Fleet Numerical Meteorology and Oceanography Center (FNMOC) is the premier provider of worldwide meteorological and oceanographic support to U.S. and coalition forces. Recently, FNMOC’s Climatology Division has received multiple inquiries from Meteorology and Oceanography (METOC) naval officers operating in the United States Fifth Fleet (C5F) Operating Area (OPAREA) during the summer season regarding dangerously hot air temperatures. Experienced temperatures are reported to be hotter than climatological guidance, which poses a risk to operations in the OPAREA.

In response, we have analyzed apparent temperature (AT) trends over the C5F OPAREA using both observations from the National Climatic Data Center (NCDC) and data from the Climate Forecast System Reanalysis (CFSRv2) dataset. Combining air temperature and humidity, AT or heat index provides a more accurate representation of what the human body experiences, especially in hot and humid conditions. In this study, we use the multiple regression analysis developed by Lans Rothfusz and described in a 1990 National Weather Service (NWS) Technical Attachment, SR 90-23. The analyses include both model and observation-based data over the 30-year (Traditional Climate Normal or TCN), 10-year Optimal Climate Normal (OCN) and 5-year OCN time periods.

Preliminary results from CFSRv2 show a huge increase in mean AT for the 5-year OCN period compared to TCN period, especially in the coastal regions of C5F, with many areas showing increases of more than 5°F. The 5-year OCN increases also exceed the 10-year OCN increases, which suggests that ATs are increasing even faster in the last few years. The results also show that both the 10-year OCN and 5-year OCN anomalies for ATs exceed the respective anomalies for air temperatures, which highlights the need to use AT instead of air temperature when considering heat risk for operations. As for the NCDC observations, our results show that ATs have also increased the most in the 5-year OCN period, with increases of up to 0.23°F/month in Bahrain.

Using a combination of reanalysis dataset and port observations, we aim to more accurately quantify the increase in heat stress experienced by the U.S. Navy forces operating in C5F and provide a more robust climatological guidance to ensure operational safety.