High wet bulb temperatures and related heatwave mass casualty events have spanned the globe during the record hot summer of 2015. Now, it appears the Southern United States is also falling under the gun of life-threatening heat and humidity.
Gulfs of Mexico, California Host Screaming Sea Surface Temperatures
As with so many recent heatwaves with the potential to produce mass casualty events, the story starts with sea surface temperatures in excess of 30 degrees Celsius (86 Fahrenheit). And across a broad region of the Gulf of Mexico and all throughout the Gulf of California ocean surface waters now feature temperatures in the range of 30 to 33 degrees C (86 to 91 F).
(A tell-tale pool of 30 C+ water is gathering in the Gulfs of Mexico and California. Such hot water is a support for deadly wet-bulb readings in the range of 30-33 C. Image source: Earth Nullschool.)
These are waters warmed by increasingly vicious human hothouse conditions. A world ocean facing a global fever that is 1 degree C (1.8 F) hotter than the more placid, less dangerous temperatures of 135 years ago.
In the Gulfs of Mexico and California, this heat has concentrated — pushing the waters there into 1-4 C above average ranges. Generating a dangerous reservoir of latent heat. One featuring ocean temperatures similar to those that kicked off heatwave mass casualty events in India, Pakistan, Japan and Egypt this summer. But this feature of the human hothouse is now focusing in on the Southern US — creating conditions that are increasing the risk of heat stress, heat injury and possibly loss of life.
The steaming waters of our southern gulfs will feed dangerously high wet bulb temperatures throughout a large region from the Carolinas to Florida through the Gulf States and on into the Southwest over the coming days and weeks. Ocean temperatures hot enough to support wet bulb readings in the range of 30 to 33 degrees Celsius. Dangerous levels very close to the maximum human threshold of 35 C.
NOAA Predicts Heat Indexes to Skyrocket
Concordantly, a similar measure used to determine how hot it feels outside is set to skyrocket throughout the southern US over coming days. In many regions heat indexes are predicted to exceed 100, 105, 115 or even 120 degree readings.
(Forecast heat index map for Monday, August 24. Over the next seven days, heat index values are predicted to remain in dangerous ranges across large sections of the Southern United States. Image source: NOAA.)
Regions at greatest risk include Southern California, Arizona, and the Gulf Coast states of Texas, Lousiana, Mississippi, Alabama, Georgia and Florida.
Heat index values in excess of 105 F (40 C) are considered dangerous. Those crossing a 127 F (53 C) threshold are considered exceedingly dangerous. The NOAA forecast now includes dangerous heat indexes predicted for the above regions lasting for at least the next seven days. And with sea surface temperatures likely to remain much hotter than average near the area of highest impact through the end of August, these high-risk heat conditions have the potential to continue for some time.
Hat tip to DT Lange