Fujiwhara and Northeast Hurricanes

On Saturday I attended the Tri-State Weather Conference out at WestConn in Danbury. Dr. Bob Hart, a North Branford native who’s a professor at Florida State University, gave a superb talk on the 1938 hurricane.

We know a lot about the 1938 hurricane. It’s been looked at and researched quite a bit. We are now able to get a new look at the storm thanks to the 20th Century Reanalysis which uses historical surface observations to recreate a ย “six-hourly, four-dimensional global atmospheric dataset spanning 1871 to 2010 to place current atmospheric circulation patterns into a historical perspective.”

Now we’re able to get a better idea what the synoptic pattern looked like during at after the 1938 storm. Here’s a look at the sea level pressure and 500 mb ensemble mean height reanalysis for12z 9/21/1938.

No big surprises here with a deep, anomalous 500mb cut off low essentially capturing the 1938 hurricane and rocketing it north. A large portion of Dr. Hart’s presentation was about 38’s unusual (and dangerous) extra tropical transition to warm seclusion and associated problems with predictability.

He also talked about the 1893 hurricane which brought a devastating storm surge to New York City. The 1893 storm took an unusual path. Instead of losing longitude as it moved north of the Carolinas is continued due north to New York City.

1893 Hurricanes #4 and #6

While 1893 Hurricane #4 barrelled toward New York City there was another hurricane nipping on its heels. The best track data shows 1893 hurricanes #4 and #6 on very different paths. On August 24 at 00z hurricane #4 was just east of Norfolk, VA while hurricane #6 was just north of Puerto Rico as caetgory 2 and 3 storms, respectively. The 20th century reanalysis data shows an impressive parade of Atlantic hurricanes but a relatively unimpressive 500 mb trough over the Great Lakes (though there is strong ridging over the North Atlantic).

 

So what lead the 1893 hurricane to smash right into New York City and not head out to sea? Dr. Hart argues the Fujiwhara effect kept Hurricane #4 close to the coast as the interaction between the 2 powerful cyclones resulted in Fujiwhara behavior. Wild stuff, right? While Fujiwhara can result in beautiful interactions in the west Pacific it is more unusual (but certainly not unheard of) ย in the Atlantic. While these 2 hurricanes didn’t make a complete loop Fujiwhara appears to have influenced the hurricanes track.

Connie and Diane in 1955 lead to one of the state’s worst natural disasters on record (see here).

While I had always noted their unusual track burps with Connie’s sharp right south of Hatteras and Diane’s sharp left southeast of Bermuda I had never really given it much thought. Hart cited this as an example of Fujiwhara interaction between the 2 cyclones.

While Fujiwhara is fun to say it can lead to a model meltdown. One of the most sobering parts of Dr. Hart’s talk was about the breakdown in predictability of a tropical cyclone’s track when Fujiwhara interaction is involved. Using the 20th century reanalysis as an initial condition the model Dr. Hart ran (I believe it was a WRF ensemble) showed exceptional spread and run-to-run variability in the 1893 case. The potential for dramatic track errors in a short period of time is alarming – particularly for the kind of storm that brought a 25 foot storm surge to New York City.

Getting a hurricane into New York or southern New England is unusual. While many follow a rather predictable pattern there are exceptions with highly anomalous flow regimes or Fujiwhara interactions that, according to Dr. Hart, can lead to breakdowns in predictability. Certainly a sobering thought from an emergency management and operational meteorology perspective.

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1955 Floods Revisited

Last week I posted about the great 1955 flood and how it did (or actually didn’t) compare to the flooding from Irene and Lee. I put together a page here on the blog in the “archive” section about the ’55 floods. The page is still a work in progress so feel free to email me or comment with any suggestions you might have.

Besides the flooding of August 19, 1955 I looked at the flood control systems that were built on the Naugatuck, Farmington, and Quinebaug rivers in the years following the great flood. These massive (and costly) projects are more examples of sizable infrastructure projects our federal government invested in decades ago. The flood control on these rivers no doubt has saved lives and saved money in the last 56 years. The investment has paid off.

I also included a special that WKNB-TV aired in 1956 about the great flood. WKNB were the call letters of channel 30 from 1953-1957. Here’s a look at the 37 minute special that included clips from a telethon channel 30 aired after the flood to raise money for victims.

 

 

Comparing Irene and Lee to Connie and Diane

Here in Connecticut many have made the comparison between the flooding after Irene and Lee in 2011 to the flooding following Connie and Diane in 1955. Both flooding events came following 2 back-to-back tropical systems. The similarities, however, stop there.

Besides the 1938 hurricane, the 1955 flood was arguably the greatest natural disaster in Connecticut since colonial times. The amount of rain that fell in August 1955 is so off the charts no event has come anywhere close to it in the last 100 years. The monthly record of 21.87″ at Bradley Airport stands alone as the wettest month on record – the second highest 16.32″ from October 2005 lags far behind.

Hurricane Connie

Hurricane Connie made landfall over the Outer Banks as a minimal hurricane on August 12, 1955. The storm moved slowly up the Chesapeake Bay and dumped 5″-10″ of rain in portions of northwest Connecticut. Connie barely produced any wind in Connecticut as she passed to the west but dropped enough rain to saturate the soil and raise river levels above flood stage.

Hurricane Diane

5 days after Connie, Hurricane Diane made landfall in North Carolina very close to where Connie struck. The storm moved inland and then was picked up by a strong trough diving into the Great lakes. An exceptional band of rain setup over northwest Connecticut and western Massachusetts as the storm passed over Long Island. 10″-20″ of rain was common in many areas. When preceded by Connie’s 5″-10″ of rain Diane’s record 24 hour rainfall was enough to push rivers to levels that hadn’t been seen in hundreds of years.

August 1955 Rain

The all-time 24 hour rain record in Connecticut occurred on August 19th in Burlington with 12.77″ falling. In Westfield, Massachusetts an incredible 1-day total of 19.75″ fell. A close up look at the 8-day rain totals from August 12, 1955 to August 20, 1955 reveal just how exceptional this flood event was.

August 12, 1955 to August 20, 1955 Rain

The 1955 floods destroyed entire neighborhoods, entire downtowns, and entire families. Waterbury, Winsted, Naugatuck, Derby, Ansonia, Farmington, New Hartford, and Putnam are just some of the towns and cities that were changed forever.

With the amount of rain that fell it’s not surprising the 1955 floods set records on the Quinebaug, Farmington, and Naugatuck Rivers.ย  The Army Corps of Engineers built a monstrous system of levees and dams on those rivers to prevent a flood like the ’55 one from happening again. Barring an unforeseen catastrophic failure of the dam and levee system a flood to the level of 1955 will never happen again on those rivers.

There’s no doubt that the combination of Irene and Lee dropped an impressive amount of rain on Connecticut. Some areas picked up 10″-15″ in a 2 week period! The fact that the Irene/Lee rain was spread out over 13 days and not the 8 days of Connie/Diane makes a big difference. The difference between 10″-15″ and 20″-25″ in a river basin is huge as well! From the time the rains from Connie ended there was only about 48 hours until the rains from Diane began.

The flooding from Irene and Lee was significant. The 1955 flood was extraordinary. The August 1955 flood and rainfall totals are to this day unrivaled. Comparing 2011 to 1955 is like comparing your average thunderstorm to an F5 tornado. It doesn’t make a whole lot of sense.

1955 Rain Totals

Barkhamsted – 25.06″

  • Connie – 9.11″
  • Diane – 15.95″

Burlington – 24.65″

  • Connie – 8.73″
  • Diane – 15.92″

Norfolk – 21.81″

  • Connie – 8.93″
  • Diane – 12.88″

Warren – 18.60″

  • Connie – 7.74″
  • Diane – 10.86″

Windsor Locks – 18.42″

  • Connie – 4.02″
  • Diane – 14.40″

Falls Village – 16.83″

  • Connie – 6.75″
  • Diane – 10.08″

Danbury – 14.83″

  • Connie – 8.74″
  • Diane – 6.09″

Hartford – 11.75″

  • Connie – 3.90″
  • Diane – 7.85″

Prospect – 10.96″

  • Connie – 3.41″
  • Diane – 7.55″

Middletown – 10.90″

  • Connie – 4.53″
  • Diane – 6.37″

Bridgeport – 8.34″

  • Connie – 5.32″
  • Diane – 3.02″