Major Gulf Hurricanes

Category 5 Hurricane Katrina on 8-29-05  (Source: NOAA)

Some of the Atlantic Ocean Basin’s strongest hurricanes such as Michael reached their peak intensity in the Gulf of Mexico.  The Atlantic Ocean Basin includes the Atlantic Ocean, Gulf of Mexico and Caribbean Sea.  Warm ocean water, often at least 80° Fahrenheit to a depth of at least 200 feet, is required for a tropical storm or hurricane to intensify under ideal atmospheric conditions. Some of the warmest water anywhere in the Atlantic Basin can be found in the Gulf of Mexico.

Smaller areas of water that features higher sea surface temperatures can sometimes influence hurricane intensity.  The Gulf of Mexico’s Loop Current is a smaller area of warmer ocean water than can influence tropical systems.  There is also something known as a “warm core ring,” which is simply an eddy or localized current of water that breaks off from the main ocean current (like the Gulf Stream or Loop Current) and can linger over an area of a few to a few hundred kilometers.  These warmer waters can provide additional fuel for an intensifying hurricane

2005: Both Hurricanes Katrina and Rita grew into two of the strongest hurricanes on record while over the Gulf of Mexico.  At peak intensity, Katrina had sustained winds of 175 mph and a minimum central air pressure of 902 millibars (mb).  Standard sea level air pressure is approximately 1013 mb and the lower the pressure, the stronger the storm is.  A few weeks later, Hurricane Rita became even stronger with sustained winds of 180 mph and minimum air pressure of 895 mb.  Fortunately, both weakened below Category 5 status but still made landfall as major hurricanes.  Rita remains the strongest hurricane on record in the Gulf of Mexico. 

  

2004: Hurricane Charley underwent a period of rapid intensification in the southeast Gulf of Mexico.  Its air pressure dropped 18 millibars and its sustained winds increased 35 mph in just a three-hour period.  This powerful Category 4 hurricane made landfall near Punta Gorda, Florida with sustained winds of 150 mph.  It was the strongest hurricane to make landfall anywhere in the U.S. since Andrew in 1992 and the strongest hurricane in southwest Florida since Donna in 1960.

1995: Hurricane Opal underwent a period of rapid intensification while over a warm core ring in the Gulf of Mexico.  In less than 24 hours, Opal went from being a minimal hurricane to a strong Category 4 hurricane with sustained winds of 150 mph and a minimum central air pressure of 916 millibars.  Although Opal weakened to Category 3 storm before its landfall in the Florida panhandle, it was nevertheless destructive and deadly.

Hurricane Opal was actually very similar to this month’s Hurricane Michael in that both occurred in October and reached virtually identical peak intensities.  Michael, however, intensified up until it made landfall with sustained winds of 155 mph and a minimum air pressure of 919 mb. 

Weather Quiz

True or False.  2018 has already become one of the wettest years on record in the Nation’s Capital with more than 51” of rain since January 1.

How Wet Has 2018 Been in DC ?

A total of 1.51” of rain fell on October 11 due to the combination of a cold front and remnants of Hurricane Michael.  It was the 19^th day since January 1 that the Nation’s Capital got more than an inch of rain.  It was also DC’s first measurable rainfall since September 28 and highest daily rainfall total since September 9 (1.59”).

Washington, D.C. has had a total of 51.55” of rain since January 1.  That’s nearly 12” more than the yearly average of 39.74”.  As of October 15, DC has an annual rainfall surplus of 19.77” of rain.  Making this rainfall total especially impressive is that January and March were each considerably drier than average in the Nation’s Capital.  Washingtonians saw a combined total of only 2.86” of rain in January 2018 and March 2018, less than half of the average total of 6.29”.  

Although February 2018 was wetter than average, it wasn’t until April that the weather pattern took a significant shift in the Nation’s Capital.  For the first time since 2003, Washington, D.C. has had at least six consecutive wetter than average months.  According to NOAA, the months of May, July and September each had more than 8” of rain.  That’s the first time on record that a calendar year has had three such wet months.  Weather records in Washington, D.C. date back to 1871.

July 2018 is another good example of how unique the rainfall has been in the Nation’s Capital. Although the month finished with 9.73”, roughly 55% of that occurred during the two-day period of July 21-22.  In fact, July 21 was one of DC’s wettest July days on record with a daily total of 4” and the month finished as the fourth wettest dating back to 1871. 

September 2018 had the most days with rain (21) in the Nation’s Capital of any month so far this year.  The period from July 15 through September 30 was exceptionally wet with rain on 48 of the 77 days resulting in a total of 24.65”.  It’s hard to imagine that DC had more than 60% of its annual average amount of rainfall in only two and a half months.  It’s also remarkable since the DC Metro Area only saw limited effects from the remnants of Hurricane Florence last month.

Washington, D.C. only needs to have average rainfall during the rest of the year for 2018 to finish among the Top 5 wettest on record.  Making that even more unusual is that 25 of the 32 months from August 2015 to March 2018 were drier than average in Washington, D.C.  The Nation’s Capital accrued a rainfall deficit of 16.42” in that time, but has a rainfall surplus of 21.03” since April 1, 2018. 

Washington, D.C.’s Ten Wettest Years (Source: NOAA)

1.  61.33” (1889)

2.  60.83” (2003)

3.  60.09” (1878)

4.  58.17” (1886)

5.  57.54” (1948)

6.  54.49” (1937)

7.  52.95” (1891)

8.  52.92” (1906)

9.  52.59” (1877)

10.  52.03” (1942)

Fall has Finally Arrived

NOAA expects cooler than average temperatures to linger in the Mid-Atlantic

Although fall officially arrived last month, September 2018 certainly didn’t feel like autumn.  Last month was one of DC’s warmest September’s on record and finished tied with 2010 for fifth warmest.  September’s warm weather lingered into October, with D.C.’s first 90° October day (October 4) since 2013.  Moreover, the first 12 days of October were the warmest on record with an average temperature (combining daily high and low temperatures) of 74.7° according to the National Weather Service.

However, a major shift in the weather pattern occurred with the arrival of a cold front on three days ago.  The combination of the cold front and the remnants of Hurricane Michael brought a total of 1.51” of rain to the Nation’s Capital on October 11.  Area residents know that September 2018 was a very wet month (D.C.’s fifth wettest on record) with measurable rainfall on eight of its final 10 days.  By comparison, the precipitation on October 11 was D.C.’s first day with measurable rainfall since September 28.

In fact, 2018 has been a very wet year in the Nation’s Capital, with a total of 51.36” of rain since January 1 (compared to the annual average of 39.74”).  January and March were each drier than average this year, so had even average rainfall occurred in those months, DC would be closer to setting a record for wettest year (1889 is the current record-holder for D.C.’s wettest year with 61.33”).  Merely having average rainfall the rest of the year would give DC a total of 59.43”, making 2018 DC’s fourth wettest year on record.  

The warm and dry start to October has come to an end.  That’s because a shift in the jet stream has enabled cooler, fall-like temperatures to take control of the weather pattern for much of the eastern United States.  Temperatures this weekend have been cooler than average.  Average high temperatures in the Nation’s Capital in mid-October are in the upper 60s.  DC’s high and low temperature of 62°/49° on October 13 was the coolest day in the Nation’s Capital since April 29 (58°/49°).  Today’s high/low temperature of 60°/48° was actually more characteristic of early November than mid-October.

NOAA expects cooler than average temperatures to continue through the remainder of the month.  However, given the record warm start to October, having cooler than average temperatures over the second half of the month should help October finish with near average monthly temperatures.

Hurricane Michael Breaks Records!

Hurricane Michael Nearing Landfall on October 10, 2018  (Source: WUSA9)

Hurricane Michael quickly developed into an intense borderline Category 4/Category 5 storm with sustained winds of 155 mph at its time of landfall yesterday.  Its minimum central air pressure fell to 919 millibars (standard sea level air pressure is approximately 1013 millibars or “mb”).  That means Michael had the third lowest air pressure of any landfalling hurricane in the United States and the fourth highest sustained winds speeds.  Michael became the strongest hurricane to ever make landfall in the Florida panhandle.  

Only three major Category 3 hurricanes (sustained winds of 111 – 129 mph) have made landfall in the Florida panhandle since 1950.  However, the Gulf Coast and inland areas are significantly more developed now than they were during past storms, making the potential for damage with Hurricane Michael significantly higher.  The three previous hurricanes (Dennis 2005, Opal 1995 and Eloise 1975) each caused enough damage to have their names subsequently retired by the World Meteorological Organization (WMO).

 

Unlike Dennis, Opal and Eloise that all weakened before making landfall, Hurricane Michael continued to intensify.  From the time Michael became a hurricane on Monday, October 8 at 11:00 a.m. (Eastern) with sustained winds of 75 mph and a minimum air central air pressure of 982 mb, it continued to intensify over the next 51 hours until it made landfall at 2:00 p.m. Eastern time October 10 with sustained winds of 155 mph and a minimum central air pressure of 919 mb.  A drop of 63 millibars and increase of 80 mph in just over 48 hours is a relatively fast rate of intensification. 

Its rapid strengthening is an important consideration since the evacuation zone for a Category 4 hurricane is much larger than for a Category 1 or 2 storm.  Naturally, larger and more widespread evacuations take more time.  That underscores the need to have hurricane preparation plans in effect at the start of each hurricane season in June.

According to weather records that date back to 1851, a total of four Category 4 hurricanes have made landfall in the United States during the month of October, with the most recent being Hurricane Hazel in 1954.  Hazel had previously been the strongest October hurricane to make landfall with sustained winds of 130 mph a minimum central air pressure of 938 millibars.  However, Michael was much stronger than Hazel at peak intensity that was reached shortly before making landfall yesterday. 

Some may recall that Hurricane Irma was a Category 4 when it made landfall in southwest Florida in September 2017.  But, Hurricane Michael was more intense with higher sustained winds and a lower air pressure.  Sometimes, there is a lag time between a very low air pressure and a commensurate increase or decrease in the sustained wind speeds of a hurricane.

Overall, Hurricane Michael’s track was well-forecast as it was expected to track northward into the eastern Gulf of Mexico.  However, given Michael’s rare intensity at landfall it will take weeks if not months to measure its impacts both on the Gulf Coast and the southeastern United States.  It’s all but certain that for a third straight year the Atlantic Ocean will have an “M” storm retired.  Hurricanes “Matthew” in 2016 and “Maria” last year both saw their names subsequently retired.

Strongest Landfalling Hurricanes in Continental United States by Air Pressure (millibars or "mb")

Source: National Hurricane Center

1.  Florida Keys Labor Day Hurricane (1935) – 892 mb
2.  Camille (1969) – 900 mb
3.  Michael (2018) – 919 mb
4.  Katrina (2005) – 920 mb
5.  Andrew (1992) – 922 mb

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Strongest Landfalling Hurricanes in Continental United States by Sustained Wind Speeds (mph)

1.  Florida Keys Labor Day Hurricane (1935) – 185 mph
2.  Camille (1969) – 175 mph
3.  Andrew (1992) – 165 mph
4.  Michael (2018) – 155 mph
5.  Charley (2004) – 150 mph

--> Hurricane Charley was the most recent of five hurricanes to make landfall in the U.S. with 150 mph sustained winds