Excessive heat not letting up this week

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PHOENIX – We're on day 10 of an excessive heat warning that originally was supposed to expire nearly a week ago. The National Weather Service has extended that warning once again so it now expires Friday night, more than a week after its initial expiration date.

The record for the most days under an excessive heat warning was nine. We are breaking that record Wednesday. The good news is that the area covered by that warning is shrinking. The Phoenix metro area, however, is still included, as is the rest of Maricopa County and north-central and northwest Pinal County.

While we’re relatively used to dry heat, that’s not what we’re seeing right now. The dew point Wednesday morning was 54 degrees. That’s fairly humid for us, and it's about the level at which evaporative coolers become ineffective.

So far, we’ve had 30 days of 110-plus-degree days, well above the average of 19 and closing in on the record of 32. That was set in 2007. Today will be day 31, and based on the current forecast, we’re likely going to tie the record at the very least.

August 2011 has been a record-breaker in more than a dozen ways, and will go down as the hottest August on record.

As of Sunday, the average daily high was 108.6, well above the seasonal average of 104 and more than a degree hotter than the previous record, which was set in 1962.

Tuesday's high of 113 at 3:21 p.m. set another record. Last year, on Aug. 30, it was just 98.

In addition to tying or breaking several daily records for highs and extra-warm lows this month, we also saw the all-time hottest day in August when the mercury climbed to 117 last Friday.

Wednesday’s high should top out at about 112 degrees in the Phoenix metro area. The overnight low will be about 89. Thursday, the first day of September, is looking to be about 110 degrees with a chance of afternoon and evening storms.

Once we get into the Labor Day weekend, it looks like it's going to be a bit cooler although still above average.

The unrelenting heat, especially those extremely warm nights, means your body has very little time to recover, which makes proper hydration more important than ever. Heat-related illnesses can sneak up on you very quickly and they can be deadly.

Records -- National Weather Service

Average daily high (through Aug. 28) -- 108.6
Previous record was 107.3 in 1962

Average daily temperature (through Aug. 28) -- 98
Previous record was 96.2 in 2007

Average daily low, warmest (through Aug. 28) -- 87.3
Previous record was 86.1 in 2007

Daily highs
Aug. 22 -- 113 (previous was 111 in 1999)
Aug. 23 -- 114 (previous was 112 in 1985)
Aug. 25 -- 113 (previous was 112 in 2001)
Aug. 26 -- 117 (previous was 114 in 2001)
Aug. 30 -- 113 (previous was 112 in 1984)

Daily lows, warmest
Aug. 24 -- 90 (previous was 90 in 2010, 2007, 1999)
Aug. 25 -- 92 (previous was 89 in 1981, 1985)
Aug. 26 -- 93 (previous was 87 in 2010)
Aug. 27 -- 90 (previous was 87 in 1998)
Aug. 28 -- 89 (previous was 88 in 2005)

All-time hottest day in August
Aug. 26 -- 117
Previous was 116 on Aug. 10, 2003, Aug. 4, 1975, and Aug. 1, 1972