Weather Quiz

True or False.

More rain fell in the Nation's Capital in July 2019 than in the nearly 2.5 months since.

October’s Hurricane Power

Hurricane Michael, October 2018  (Source: NOAA)

Although September is the busiest month of the Atlantic hurricane season, the tropics often remain active well into October.  Some of the most powerful hurricanes on record have occurred in October, including several Category 5 hurricanes.

2018 – Hurricane Michael became only the fourth Category 5 hurricane to make landfall in the United States.  It was the first to do so since Hurricane Andrew 26 years earlier and it remains one of the few hurricanes that intensified up until its landfall.  Michael reached its peak intensity as it made landfall along the Florida panhandle with sustained winds of 160 mph and a minimum central air pressure of 919 millibars (mb).  That part of Florida had seen several Category 3 hurricanes, but never a Category 4 or 5 storm.

2016 – Hurricane Matthew was the first Category 5 hurricane to develop in the Atlantic Ocean since 2007.  That’s not to say there weren’t multiple destructive and deadly hurricanes during that time frame such as Ike, Irene and Joaquin, but none had reached Category 5 intensity.  Matthew had sustained winds of 165 mph and a minimum central air pressure of 934 millibars at its peak intensity.

2005 – This season broke virtually every hurricane record that was on the books for the Atlantic Ocean.  Prior to 2005, no more than two Category 5 hurricanes had developed in a single season.  Hurricane Wilma was not only the fourth, but it became the strongest hurricane on record for the Atlantic Ocean Basin.  At peak intensity, Wilma had sustained winds of 185 mph and a minimum central air pressure of 882 millibars.  That broke Hurricane Gilbert’s 1988 record of 888 mb.  Wilma made landfall on the southwest coast of Florida as a Category 3 storm.

1998 – Hurricane Mitch set several important benchmarks during its existence.  It ended a modest six-year stretch without a Category 5 hurricane in the Atlantic, being the first since Andrew in 1992.  Mitch was also the Atlantic’s first October Category 5 since “Hattie” in 1961.  At peak intensity, Mitch had sustained winds of 180 mph and a minimum air pressure of 905 millibars.  Mitch caused devastating flooding in Central America that claimed more than 10,000 lives. 

Feeling More Like Fall

Although October got off to a sizzling start in the Nation’s Capital with four hot days, this weekend has felt much more like autumn.  Nevertheless, Washingtonians have had an exceptional start to October with a temperature spread of nearly 50° in the span of three days.

The high temperature in Washington, D.C. reached a July-like 98° on October 2.  That not only obliterated the previous daily record high of 89°, but it also set a new record for DC’s hottest overall October temperature.  It was also DC’s 62^nd day of 90° heat of 2019.  That puts this year solidly in second place for highest annual total of 90° days behind only the total of 67 days that occurred in 2010 and 1980.  The Nation’s Capital averages only 36 days of 90°/+ in a given year.  By comparison, DC had an above average but much lower total of 45 days of 90° heat last year.

Yesterday’s high temperature of 67° at National Airport was DC’s coolest high temperature since May 14 (64°).  The low temperature of 49° yesterday was also the coolest temperature in the Nation’s Capital since April 29 (47°).  Those temperatures are common in the DC Metro Area in the fall, but not for a few more weeks.  For example, DC’s average high/low temperature on October 19 is 67°/49°.

Although Washingtonians often see the final day of 90° heat of the year in September (13 of the last 26 years), October has now had 90° heat six times since 1993.  The first frost of the fall season doesn’t typically occur within Washington, D.C. city limits until the second week of November.  However, the northern and western suburbs often see frost in mid-to-late October.  Fall allergy sufferers actually look forward to the first frost of the fall since it eliminates many environmental allergens such as ragweed and grass pollen.

Measurable snowfall has also occurred in the Nation’s Capital on more than one occasion during the month of October.  DC’s earliest accumulating snowfall of the season occurred on October 10, 1979 (0.3”).  However, having a significant amount of snowfall before December 31 doesn’t always correlate to a cold and snowy winter.  A good example of this occurred during the 1989-1990 winter season.  Washingtonians had a combined 12.5” of snow in November and December but less than 3” occurred the rest of the winter.

Temperatures will be milder today compared to yesterday with high temperatures in the 70s.  NOAA’s Climate Prediction Center expects near average temperatures to continue in the DC Metro Area through the middle of the month.  DC has a rainfall deficit of nearly 5” since August 1 and that’s contributed to moderate drought conditions for a significant portion of the DC Metro Area.  While some showers are possible tomorrow evening, no significant rainfall is expected.

Record Heat Coincides with October’s Arrival

Fall is a great time of the year in the DC Metro Area

September 2019 finished as DC’s third warmest on record with an average monthly temperature of 76.5° (combining daily high and low temperatures).  Five of DC’s 10 warmest September’s have now occurred since 2005.  Last month was also poised to finish tied with September 2005 for DC’s driest.  However, 0.14” of rain on September 30 caused last month to finish as DC’s fourth driest with 0.25”.  Monday’s rainfall also ended a 17-day stretch without measurable rainfall in the Nation’s Capital.  Last month was DC’s driest overall month since March 2006 (0.05”).

October has picked up where last month left off with record heat on tap today with highs in the low to mid 90s for the DC Metro Area.  There’s also a chance DC could set a new record high today for the entire month of October.  DC’s hottest October temperature on record is 96° and occurred way back on October 5, 1941.  Although Washingtonians experienced one October day with 90° heat last year, there have been only five Octobers with such unusual heat in the last 25 years.  That includes October 2007 when DC had a highly unusual heat wave with three days of 90° heat from October 7 – 9.  

Average high and low temperatures fall throughout the month of October from 74°/56° on October 1 to 64°/46° on October 31.  DC’s coldest October temperature of 26° occurred twice, most recently on October 31, 1917.  There has been a nearly even split with 11 of the last 20 Octobers that were warmer than average in Washington, D.C.

The Nation’s Capital averages 3.4” of rain during the month of October.  Although the last four October’s have been drier than average in Washington, D.C., there has been an even split with 10 of the last 20 Octobers having been wetter than average.  While last month fell just short of tying DC’s 2005 record for driest September, many comparisons have been made since both Septembers were significantly warmer and drier than average.  It’s worth pointing out that October 2005 featured a major shift in the opposite direction from the previous month and finished as DC’s wettest on record.

NOAA’s outlook for October 2019 doesn’t call for a significant deviation from normal rainfall in the Nation’s Capital.  It shows an equal chance for above or below normal rainfall with an elevated potential for below average rainfall in parts of southern Maryland and Virginia.  Significantly warmer than average temperatures are expected for the month.  That doesn’t mean there won’t be some chilly, fall-like weather at times this month; but October as a whole is expected to finish as a warmer than average month in the Nation’s Capital. 

October 2 Record Highs (Source: NOAA)

National Airport, Washington, D.C. (DCA): 89° (1986, 1881)
Dulles Airport, Sterling, Virginia (IAD): 89° (1986)
BWI Airport, Baltimore, MD: 89° (1986)

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All-Time October Record Highs (Source: NOAA)

DCA: 96° (October 5, 1941)
IAD: 94° (October 9, 2007)
BWI: 97° (October 5, 1941)

Hurricane Season Update

Hurricane Lorenzo near peak intensity  (Source: NOAA)

If the 2019 Atlantic hurricane season were to end today, then it would essentially finish with an average number of named storms.  There have already been 12 tropical storms of which 5 became hurricanes, including three major hurricanes.  Although June and July were predictably quiet months in the tropical Atlantic, the first named storm of the season (Andrea) developed before June 1 for a record fifth consecutive year.

NOAA was expecting a near average hurricane season when it began on June 1.  However, once the weak episode of El Nino dissipated early in the summer NOAA revised its forecast in early August.  El Nino conditions tend to correlate with less favorable conditions for tropical development in the Atlantic Ocean Basin.  So it wasn’t a surprise than NOAA’s updated forecast called for a slightly busier than average hurricane season.

The two most significant Atlantic storms of the season to this point have been Hurricanes Dorian and Lorenzo.  Both achieved Category 5 intensity and that made 2019 the fourth consecutive year one has developed in the Atlantic Ocean.  The previous record for most consecutive seasons with a Category 5 hurricane was three, from 2003 – 2005.  Although Dorian devastated parts of the Bahamas at peak intensity, it weakened considerably before impacting the southeastern U.S. coastline.  Nevertheless, Dorian still had significant impacts in the United States.

While not a threat to the United States, Lorenzo remains a noteworthy storm for becoming the easternmost point an Atlantic hurricane has reached Category 5 intensity (45°W).  It also put this season in relatively rare company as one of a total of only seven seasons with at least two Category 5 Atlantic hurricanes (1932, 1933, 1961, 2005, 2007 and 2017).  This is the fourth time “Lorenzo” has been a named storm in the Atlantic Ocean Basin and the 2019 version is easily the most intense.

Tropical storms and hurricanes only develop when atmospheric and environmental conditions are favorable.  September is the busiest month of the Atlantic hurricane season so it’s common to see hurricanes develop.  October is also an active month of the hurricane season that’s seen a number of significant storms such as Hurricanes Mitch, Wilma and Matthew.  While all three reached Category 5 status, none of them impacted the United States at that intensity.  It remains to be seen how busy the rest of the Atlantic hurricane season will be before the season ends November 30.

Weather Quiz

True or False. 

No September in the Nation’s Capital has had a Top 10 finish for both warmest and driest on record.  Weather records in Washington, D.C. date back to 1871.

Late Season 90° Heat

NOAA's Temperature Outlook for the Second Week of October

Temperatures in the Nation’s Capital have reached the 90s on eight days so far this month.  That’s the highest such total since September 2010 when Washingtonians sweat through 10 days of 90° heat.  Two record high temperatures have also been set at National Airport this September for the first time since 1991.

The frequency of the 90° heat has been spread out fairly evenly throughout September.  There haven’t been more than two consecutive days of 90° heat in the Nation’s Capital since September 1.  That means there haven’t been any “heat waves” which are defined as a minimum of three or more consecutive days of temperatures at or above 90°.  It is somewhat ironic that September 2019 has been so warm in the DC Metro Area without an official heat wave.

NOAA’s Climate Prediction Center expects these warm temperatures to continue into early-to -mid October for much of the DC Metro Area.  Another day or two of 90° heat is even possible during the upcoming work week.  Any 90° heat in the Nation’s Capital in October is a very rare occurrence.  That’s because the sun angle is much lower than during the summer months.  That combined with the decreasing amount of daylight makes it more difficult to get very warm.  The latest in the year Washingtonians have experienced 90° heat is October 11.

There have been only five Octobers dating back to 1994 that DC residents have had temperatures in the 90s.  The most recent occurrence was on October 4, 2018.  Over the same 25-year time period, DC’s last 90° day of the year occurred in August eight times, most recently in 2011.

September 2019 is well-positioned to finish as one of DC’s warmest on record.  That’s because all but five days since September 1 have been warmer than average.  This month will also finish as one of DC’s driest.  That will make this month the first time the Nation’s Capital has had a September that’s ranked among both the top five warmest and driest.