Beware the “I” Storms

Hurricane Ike, 2008  (Source: NOAA)

Tropical Storm Isaias was named July 29 and became the earliest “I” storm on record in the Atlantic Ocean Basin.  It was the fifth named storm this month, which tied July 2005 for busiest on record.  Last night it was upgraded to hurricane status and became the second Atlantic hurricane of 2020.  The United States has felt the impacts of some significant “I” storms during the last 20 years.  In fact, the “I” storm has been retired nine times since 2001!

2011: Irene was the first major hurricane of 2011, peaking as a Category 3 with sustained winds of 120 mph.  However, Irene weakened to Category 1 status before its first landfall in North Carolina.  Its impacts were far reaching from the Mid-Atlantic to New England.  According to the National Hurricane Center, Irene remains the fourteenth costliest hurricane on record in the United States ($13.5 billion in damage - adjusted for inflation).

2008:  Ike was a Category 4 hurricane with sustained winds of 145 mph and a minimum air pressure of 935 millibars (mb).  By comparison, standard sea level air pressure is approximately 1013 mb.  Fortunately, it weakened to a strong Category 2 storm with sustained winds of 110 mph by the time it made landfall in Texas.  Since Ike had a very large diameter and traveled across the entire Gulf of Mexico, it was able to build up a very impressive storm surge when it made landfall.  It did approximately $30 billion in damage at the time, making it the sixth costliest hurricane on record.   

2004: Hurricane Ivan was the strongest hurricane of a busier-than-average hurricane season.  It was a Category 5 storm that caused significant damage to Jamaica, the Dominican Republic and the Cayman Islands.  It remains one of the strongest hurricanes to form in the Atlantic Ocean.  At peak intensity Hurricane Ivan’s lowest air pressure was 910 millibars and highest sustained winds around the center of the storm were 165 mph.  Air pressure is considered a more accurate measure of hurricane intensity than wind speed.

Fortunately, Ivan weakened to Category 3 intensity before it made landfall in Alabama on September 16.  Nevertheless, it caused nearly $20.5 billion in damage at the time.  That made Ivan the 10th costliest U.S. hurricane on record.  Ivan is also significant since it set a record for spawning more tornadoes in the United States than any other tropical storm or hurricane.

2003: Isabel was the first Category 5 hurricane in the Atlantic Ocean since 1998.  Hurricane Isabel reached its peak intensity on September 11, with maximum sustained winds of 165 mph combined with a minimum central air pressure of 915 millibars.  Isabel weakened to Category 2 intensity with sustained winds of 105 mph before making landfall in North Carolina on September 18.  Despite weakening, Isabel caused major flooding and damage across much of the Mid-Atlantic Region and Northeastern United States.  In the DC Metro Area, Isabel caused approximately one million power outages.  In all, Isabel caused about $5.5 billion in damages in 2003.

Record-Setting Heat ?

The Nation’s Capital set a new record for highest total number of 90° days during the month of July.  Yesterday’s high temperature of 93° was the 26^th day of 90° heat since July 1 and that broke the previous record of 25 days set during July 2011.  It’s also DC’s record for most 90° days in any month.  What has made this month’s heat unusual is the lack of extreme heat – no record highs or 100° heat.

It’s remarkable that 31 of the last 33 days have featured high temperatures in the 90s without any triple-digit heat, dating back to June 26.  With the exception of July 24, every other day this month has been warmer than average in Washington, D.C.  These consistent above average temperatures put July 2020 in position to finish among DC’s four warmest July’s on record. 
 

July 2020 finishing as one of DC’s hottest months on record is quite a feat all by itself.  However, making it even more interesting is that the existing list of the five warmest July’s have all had at least one day of 100° heat.  For example, during July 2012 there were eight days when high temperatures reached the 100s.  DC’s previous record for most 90° days of 25 from July 2011 is also significant since that remains DC’s warmest July.  It finished warmer than July 2012, despite having fewer days of triple-digit heat (five days vs. eight).  The difference, however, were warmer overnight low temperatures in July 2011 vs. July 2012. 
 

There will likely be a tangible difference in average low temperatures at National Airport when the National Weather Service updates its running 30-year average of temperatures at the end of the year to reflect the period of 1991-2020, thus replacing the current period of 1981-2010.  Overnight low temperatures have been warmer than average on all but two days since July 1, when they fell to the daily average.  According to NOAA, DC’s lowest temperature this month of 71° is its warmest monthly low temperature on record.  If Washingtonians don’t experience a temperature below 71° before the end of the month, then that will be another warm weather record set in July 2020.

This month is well-positioned to finish as DC’s third warmest July.  DC’s average temperature (combining daily high and low temperatures) through July 28 is 84.1°.  Some minor fluctuations above or below that are possible during the final few days of the month, but not enough for it to catch July 2011 for first place at 84.5°.  

DC’s Warmest July’s By Average Temperature (Source: NOAA)

1.  84.5° (2011)
2.  84.1° (2020 – as of July 28)
3.  84.0° (2012)
4.  83.1° (2010, 1993)
6.  83.0° (1999)
7.  82.7° (2016)
8.  82.6° (1987)
9.  82.3° (1980)
10.  82.1° (2019, 1955)

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DC’s Most 90° July Days (Source: NOAA)

1.  26 (2020 – as of July 28)
2.  25 (2011)
3.  24 (1993, 1987)
5.  23 (2016, 1988)
7.  22 (2019, 2012, 1999, 1994)

Watch Out For Hanna

Hurricane Hanna nearing the Texas Coast  (Source: NOAA)

The National Hurricane Center officially upgraded “Hanna” to hurricane status this morning as it approaches the southern Texas coast.  Hanna is noteworthy for being the first hurricane of the 2020 Atlantic hurricane season.  It is also the first hurricane to form anywhere in the Atlantic Ocean Basin since Pablo in late-October 2019.  While only a Category 1 as of this writing, it could reach Category 2 intensity with sustained winds of at least 96 mph given its slow forward movement and a favorable environment for intensification.

Not having a hurricane during the first two months of the Atlantic hurricane season isn’t unusual as June and July are typically among the quietest times in the tropics.  However, this season has already set several benchmarks with the earliest C, E, F, G and H named storms.  Prior to Hurricane Hanna, all of the previous tropical storms were relatively weak and short-lived.  Part of that could be attributed to the influx of Saharan dust that created unfavorable conditions for tropical development.

The 2020 hurricane season was forecasted to be busier than average by scientists at both NOAA and Colorado State University.  A key reason is the anticipated development of La Nina conditions by the fall.  However, that wouldn’t directly contribute to the fast start to the season. What’s been favorable is warmer than average sea surface temperatures across much of the western Atlantic, Gulf of Mexico, and Caribbean Sea. 

Given the fast start to the season, Colorado State upped its seasonal forecast slightly in early July.  NOAA will update its seasonal forecast in early August.  Some comparisons have been made between the fast start to this season and the record-breaking 2005 season.  That’s when an Atlantic record of 28 tropical storms, including 15 hurricanes, developed.  Seven named storms developed in June and July of 2005.  However, unlike 2020, three of those storms became hurricanes, including major hurricanes Dennis and Emily.  By comparison, only one hurricane has developed so far this season.

The 1997 Atlantic hurricane season also had a busy month of July with a total of four tropical storms, including one hurricane (Danny).  However, unlike in 2005, or what experts expect this season, the 1997 season was quiet overall due to a powerful episode of El Nino that developed.  Once Hurricane Danny weakened in late-July, the Atlantic didn’t see another named storm until September 1997.  It’s exceptionally rare for the entire month of August to pass without a single named storm in the Tropical Atlantic.

When Hurricane Hanna makes landfall in Texas this weekend, it will the first July hurricane to do so since Dolly in 2008.  It will also be the first hurricane to make landfall in Texas during any month since Harvey in 2017.