September, 2023 opens with temperatures on the rise

Building weekend heat rises, strengthening “SW” winds into Chicago, defeating lake cooling. Humidities to “take off” Monday, Tuesday and Wednesday

Thursday with lows of 54 degrees at both of Chicago’s major city airports, O’Hare and Midway. Not since a 53-degree minimum the morning of June 17th has it been cooler.

AND THERE WERE CHILLIER READINGS AWAY FROM THE CITY AND LAKE MICHIGAN

Thursday morning lows dropped to 37 degrees as close by as Sparta, Wisconsin—215 miles to Chicago’s northwest.

CHECK OUT THESE THURSDAY MORNING LOWS in and surrounding the Greater Chicago area

Hurricane expert Dr. Jeff Masters is out with a fascinating article in Yale Climate Connections on the likely impact of the warmer than normal ocean waters over which Hurricane Idalia traveled on the storm’s intensity.

• Masters notes the notion warmer ocean temps strengthen hurricanes’ winds dates back to at least 1987 when MIT (Massachusetts Institute of Technology) researcher Dr. Kerry Emanuel theorized every 1-degree Celsius ocean temps increased hurricane wind speeds by 5%. Subsequent research and computer modeling has found Emanuel’s reasoning sound, slightly reducing the actual wind increase to around 4% for every degree Celsius ocean temps rise.
• As Masters’ notes a 4 to 5% increase in wind speed may sound tiny, but he points out such an increase IS NOT TINY AT ALL. The impact on the ability of a hurricane to damage is profound and significant.
• NOAA, parent agency of the National Weather Service, shows the increase in the damage a hurricane’s winds produce is EXPONENTIAL. As an example, a CAT 2 hurricane with 100-mph winds produces ten times the damage of a CAT 1 hurricane with 75 mph winds. In other words, increasing hurricane-wind velocities by 1.3+ times from 75 mph to 100 mph produces ten times the damage. As Masters notes, “This includes damage not only from winds but also from storm surge, inland flooding and tornadoes.”
• NOAA notes the temperature of the Gulf waters over which Hurricane Idalia traveled and rapidly intensified averaged 1 to 2-degree C above the long term averages. On that basis, Idalia’s winds were likely at least 40 to 50% stronger, concludes Masters, than they might otherwise have been.
• When such a storm’s winds increase, so does its storm surge when it reaches land. The winds also deliver more moisture faster to an area, increasing rainfall.
• READ DR. JEFF MASTERS FULL “YALE CLIMATE CONNECTIONS POST” here:
• IN A SEPARATE POST Wednesday, Masters (https://twitter.com/DrJeffMasters) noted: “Idalia — 1 of 10 historical storms since 1950, intensifying at least 40 mph in the 24 hours before U.S. landfall. Sobering to see five of those storms occurred in the past seven years. Climate change increases the odds of rapid intensification. https://nature.com/articles/s41467-019-08471-z#ref-CR7“

HEAT ON THE WAY FOR THE LABOR DAY HOLIDAY WEEKEND, INITIALLY WITHOUT ELEVATED HUMIDITIES, BUT HUMIDITY TO FOLLOW MONDAY THROUGH WEDNESDAY

Chicago has entered a record long string of rain-free August days, closing the books on a month with just 31% of its normal rain and a rank of 20^th driest of the past 153 Augusts.

• Welcome to September 2023! We closed the books on August 2023 overnight at midnight ending with a 14-day RAIN-FREE STREAK in Chicago. Only 1.33” of rain fell in August, typically our 2nd wettest month of the year—a fraction of the 4.25” of rain considered normal. That means just 31% of the month’s “normal” rain fell in August—a near 3″ shortfall.
• September is to open as August closed—DRY! But a huge pattern change will see an abnormally strong DOME OF HEAT DEVELOP over the area. The coming weekend is to average 11 degrees warmer than last weekend with highs in the 90s.
• The heat is to arrive amid only modest levels of humidity. That’s important, because dry air cools far more efficiently at night. And, low humidity air allows our bodies to cool through a process known as evaporative cooling. BUT, humidities will surge going into next week with dew points building to the mid-60s Monday and to within striking distance of 70 degrees Tuesday, Wednesday and Thursday, indicating a VERY MUGGY LEVEL OF ATMOSPHERIC MOISTURE.

A NOTE ON JUST COMPLETED METEOROLOGICAL SUMMER AND THE MONTH OF AUGUST: BOTH HAD TEMPS WHICH FELL AMONG THE WARMEST FIFTHS OF THE 153 YEARS OF AUGUST AND SUMMER TEMPS SINCE 1871

• We managed to miss much of the extreme heat which has so persistently baked so many other regions of the country in recent months. But, Chicago still managed a METEOROLOGICAL SUMMER TEMP which ranked 31 warmest of the past 153 years, placing it among the 20% warmest June, July and August periods on the books. And, AUGUST was the 33rd warmest in 153 years, ranking among the warmest 22%.