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Forty and One South Florida Nights

Even Scheherazade, the legendary storyteller from “One Thousand and One Nights,” might find temperatures uncomfortable during this remarkable year of heat in Florida. The southern third of the peninsula in particular is in the midst of an improbably warm stretch, with Miami having set record warm minimum temperatures in five of the past six nights; Key West in nine of the last 10; and Fort Lauderdale for an amazing nine straight nights! Continuous temperature records in the city date back to 1912, while for Miami they reach as far back as 1896, and for Key West all the way to 1872.

As you might imagine, this streak has led to the warmest start to November on record. But this applies not just to southern Florida. A week into the month, every single Florida city had November 2015 ranked as the warmest on record.

Record warmest start to November has spread to cities in 7 states, and still covers all of #Florida #climate pic.twitter.com/NDMkWmlhh1

— Eric Blake (@EricBlake12) November 8, 2015

Forty one new record warm minimum temperatures have been set so far this year in Fort Lauderdale — also known as the “Venice of America.” Two of these set new monthly records for warmest nights (May and November). In a year widely expected to be the warmest ever measured at a global scale, there are seven Florida cities on pace for their hottest year, too: Miami, Fort Lauderdale, Vero Beach, Moore Haven, Punta Gorda, Saint Petersburg and Apalachicola. Three others — Orlando, Tampa and Daytona — are on pace for their second warmest year on record.

Because it’s been so warm so late in the year, Miami has surpassed the record date for the latest arrival of cooler air in the fall. Previously, Nov. 5, 1995 held the record for the latest time in autumn that the temperature dropped to 70°F or cooler. As I write this on Nov. 9, we are still awaiting for some relief to what feels like summer heat and humidity. Using that 70°F threshold, Eric Blake, a National Hurricane Center researcher and Florida weather afficianado, constructed the graph below of the of the length of the warm season. It shows that the duration of the warm season has lengthened significantly. One hundred years ago the warm season (without 70°F or cooler readings) lasted two months. Now it lasts five months.

That there is a likely contribution from global warming to the balmy year in Florida should come as no surprise. But there are other important factors to consider. The most important is probably the urban heat island effect that has developed in the Miami-Fort Lauderdale area. An urban heat island is a metropolitan area that has become significantly warmer due to human activities (like modification of land surfaces and energy usage). It tends to manifest itself more at night. A University of Georgia study published in the journal Computers, Environment and Urban Systems this year found that the South Florida metro area ranked first in the country in the warmth generated by the urban heat island.

Fascinating how much longer #Miami stays =>70 than before: from ~2 months 100 years ago to ~5 months now #climate pic.twitter.com/vSLlYYQn7l

— Eric Blake (@EricBlake12) November 6, 2015

This graphic below illustrates the urban heat island effect quite well. Looking at the length of the warm season, the map shows an unmistakable bulls-eye around the Miami-Fort Lauderdale area, indicating where in Florida the warm season has lengthened the most. There are some parts of north central Florida where the warm season has actually become shorter since 1950.

One more warming factor worth mentioning is the sea surface temperature in the vicinity of southern Florida, which is running a good 1-2°F above normal.

With the urban heat island permanently installed and global warming accelerating, South Floridians may see less pleasant “cool season” weather in years to come. For now, we can’t wait another night for a cold front to bring some relief.