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Last week's heavy rain and Harvey approaching hurricane strength

By: sullivanweather , 11:54 AM GMT en Agosto 20, 2011

The Rainfall which fell on the region last Friday night was particularly heavy along the coastal plain, where development of a coastal front/low pressure aided in low-level convergence. Cold air moving in aloft in the form of a very tightly would (especially for August) mid/upper-level low pressure system promoted convective elements within the overall shield of heavy rain, combined with unidirectional flow, this led to some rather impressive totals.

NASA MODIS Terra image of the Northeast on August 14th depicting a convective band of heavy rain along the coast.

Rainfall totals tapered inland, further removed from best forcing/moisture but 1-4" totals weren't uncommon up the Hudson Valley and points east into interior New England. Here's a brief rundown of some of the higher rainfall totals over the last four days:

Lido Beach, NY - 10.87"
Seabrook Farms, NJ - 10.64"
Wantagh, NY - 10.54"
West Islip, NY - 9.18"
Oceanside, NY - 8.75"
JFK Airport - 7.80" (all-time greatest daily rainfall - 8/14)
Central Park, New York City, NY - 6.37"
Lyndhurst, NJ - 6.00"

How does this event stack up against historical extreme rainfall events across the region?

April 2007 nor'easter

The last such widespread extreme rainfall event for the region affected by this latest system occurred during the April 2007 nor'easter, a slow-moving intense nor'easter which will be mostly remembered for the heavy wet snow dumped across upstate New York, northeast Pennsylvania and interior New England. But this storm did have a very wet side to it and the rainfall totals across the coastal plain were quite impressive, especially for a cold-season system. Rainfall totals as a whole were very similar over much the same area as what occurred this past weekend. However, due to the stratiform nature of the precipitation rainfall amounts were more evenly distributed than with this most recent event.

Radar rainfall estimates of precipitation during the April 2007 nor'easter

Rivervale, NJ - 9.30"
Central Park, New York City, NY - 8.41"
East White Plains, NY - 8.22"
West Shokan, NY - 7.43"
Lambertville, NJ - 7.25"
Somerset, NJ - 6.73"
Bakersville, CT - 6.72"
Roxborough, PA - 6.22"

Upton WFO PNS report of April 2007 nor'easter
Mt.Holly write-up/PNS of April 2007 nor'easter

However, for the Northeast as a whole, there's been other even more impressive rainfall events over the last ten years which make the latest event pale in comparison. June of 2006 was one such event.

June 2006 flooding

Over a 6 day timespan (24-29th) an oscillating band of heavy rain moved into the Northeast, hitting Pennsylvania and New York the hardest. Record river crests occured at many gauge sites on all 3 main stem rivers in this area (Deleware, Hudson and Susquehanna) as 5-14" of rain fell. Along the Deleware River the flooding was particulaly bad with many locations receiving a '100-year flood'.

June 2006 precipitation departures
Binghamton, NY Case Study: June 2006 Flood
Binghamton, NY June 2006 Flood page(including photos, precipitation estimate graphics and river gauge data)
Plot of rainfall amounts - New Jersey, eastern and central Pennsylvania, southeast New York, Deleware and northeast Maryland.

October 2005 flooding

Just eight months prior to the big June of 2006 flood, in October of 2005, there was a very similar atmospheric set-up which led to the most recent rainfall event; a slow-moving series of upper level disturbances moving over an area of high tropical moisture and numerous low-level convergent boundaries. This pattern repeated over a period of more than a week with two separate rainfall events, one from October 7-9th and the next from the 11-15th. Up to a foot of rainfall fell during the first system across parts of southeast New York while the second system, or series of systems, produced another widespread 5-15" of rain across the region. Central Park finished the month with 16.73", just short of breaking the all-time monthly record for rainfall of 16.85" set way back in September of 1882.

Upton WFO PNS of the Oct 7-9th event
Upton WFO PNS of the Oct 11-15th event

Flooding of late summer 2004

The most impressive widespread monthly rainfall over the Northeast over the last ten years, and on record, occurred during a period spanning August and September of 2004. The flooding was due to a series of 5 remnant tropical systems: Gaston, Hermine, Francis, Ivan and Jeanne. Each one of these systems produced some level of flooding and created wet antecedent conditions for the following systems, exacerbating the flooding problems.

Graph showing Northeast region rainfall since 1895. Note 2004 recorded the record highest basin-wide rainfall for the period of record with an 11.48" average.


Gaston rainfall amounts

Although Gaston affected the region in late August, it layed the groundwork to what the pattern would be like the the rest of the month, remnant tropical systems interacting with cold frontal boundaries to produce copious amounts of rainfall.

Gaston made landfall as a category 1 hurricane along the South Carolina coast. The storm then turned northward, then northeastward and exited the coast near Ocean City, Maryland and continued out to sea. Although the storm never made a direct impact on the Northeast, the moisture from this system became entrained into a cold front to produce localized rainfall amounts of 3-6 inches causes numerous flash floods.

Major flash flooding took place in Westbrookville, NY, a small village along the Sullivan County/Orange County border in southeast New York. Large sections of US route 209 were washed away along with many mobile homes in a trailer park. Further north in upstate New York the counties of Onondaga, Cayuga, Madison and Steuben all received significant flash flooding.


Hermine was a weak tropical storm which moved ashore Massachusetts on the last day of August. For the most part Hermine was a non-entity, producing up to 2 inches of rain over eastern Long Island and southeastern Massachusetts. There were some reports of minor basement flooding but that was the extent of her damage. Hermine formed from the same trough of low pressure that formed Gaston and oddly enough made landfall in the general vicinity as Hurricane Carol did 50 years prior.


Hurricane Frances

Frances was a long-lived Cape Verde hurricane that made 2 U.S. landfalls in Florida. One as a category 2 hurricane and another as a tropical storm in the Panhandle. The storm then turned towards the north and rode the west side of the Appalachian Mountains along a cold front before moving up the St. Lawrence River Valley.

Most of the rainfall from Frances that fell on the Northeast fell across the western half of the area with a few localized spots in southeast New York receiving heavy amounts of rain as well. Across western sections of New York and Pennsylvania 3-6" of rain fell, which brought sharp rises to areas rivers and brought some flashier creeks and streams out of their banks.

For the rest of the Northeast Frances brought a soaking rainfall which prepped the ground for Ivan, which followed one week later. There was one other area of heavy rainfall from training convection ahead of the cold front in southeast New York State which hit Orange, Putnam, Dutchess and Ulster counties hard, bringing flash flooding.

Rainfall amounts from Frances in my local area.
National Hurricane Centers' tropical cyclone report on Frances


Northeast rainfall totals from Ivan

Ivan was another long-lived Cape Verde hurricane which reached category 5 on 3 different occasions and accumulated the 2nd highest ACE for any Atlantic hurricane on record. Ivan made landfall on the Gulf Coast of the U.S. moved northward to the central Applachians before turning east, moving offshore the Delmarva. Ivan lost tropical characteristics overland, but once offshore the East Coast, moved southward before looping back towards the west. The remnants of the system then moved over Florida where it gradually regained tropical characteristics before becoming a tropical storm yet again in the Gulf of Mexico, making its final landfall in Louisianna.

For the Northeast, Ivan brought widespread heavy amounts of rain. Almost the entire state of Pennsylvania received 3 inches of rain or more, with several locations getting as many as 7 inches. With wet antedecent conditions from Gaston and Frances, flooding became a major issue. Many small streams and creeks as well as main stem rivers were brought out of their banks due to the excessive amounts of rain on saturated soil.

NWS Local forecast office links:

NWS Binghamton, NY

Radar rainfall estimates
Flooding photos
Damage reports/spotter reports

NWS Albany, NY

Multi-sensor precipitation estimate

NWS Upton, NY (NYC)

Spotter rainfall reports

NWS Tuanton, MA

24 hour rainfall 9/18/2004
24 hour rainfall 9/19/2004

NWS Mt. Holly, NJ (Philadelphia area)

Ivan rainfall page
Includes a plotted rainfall map and Public Information Statement

NWS State College, PA

Ivan Storm Summary
-This is a very informative link on the impacts of Ivan on central Pennsylvania. This link includes an in depth storm summary(text), plotted rainfall map, individual spotter reports, satellite and radar imagery, tornado reports and river stage charts for many gauge locations including river crests from Ivan, historical record crests and a comparison to the January 1996 flood.


Northeast rainfall amounts - Jeanne

Jeanne developed from a tropical wave just east of the Lesser Antilles and eventually became a category 3 hurricane, striking Florida in the same spot as Hurricane Frances 3 weeks prior. Jeanne followed an unusual path, seemingly headed out to sea after turning north, north of Hispainola. However, a strong high developed to Jeannes' north, blocking this cyclone from recurving and eventually turning her towards the U.S. East Coast. Jeanne, after making landfall, stayed inland moving up the Floridian Peninsula and up the east side of the Appalachian Mountains before moving offshore the Delmarva Peninsula.

In the Northeast rainfall from Jeanne was not as widespread as Ivan or Frances, but with saturated ground areas that did recieve rainfall quickly flooded. For the most part rain was confined to the southeastern half of the Northeast with the Philadelphia-New York City metro area hardest hit with totals of 4-7". This stripe of heavy rain continued eastward across Long Island, Nantucket, Martha's Vineyard and Cape Cod.

Jeanne related links:

HPC Jeanne Rainfall synopsis

NWS WFO State College, PA
Another very informative look into Jeannes' impacts across central Pennsylvania.

NWS WFO Mt. Holly, NJ
Includes a radar estimated precipitation map, tornado information and storm damage photos.

Pubilc Information Statement detailing spotter reported rainfall amounts.

NWS WFO Taunton, MA
24 hours rainfall 9/29/2004
24 hour rainfall 9/30/2004

Current watches, warnings and advisories.

Eastern US current watches/warnings
Current watches, warning and advisories issued by the National Weather Service. Courtesy of NOAA.


Tropical Update

As of the August 20th 4AM CDT National Hurricane Center advisory, Tropical Storm Harvey is located at 16.4°N, 86.5°W, with a westerly forward motion at 12mph. This location places the center about 10 miles northeast of Roatan Island, north of the Honduras coast. Maximum sustained winds have strengthened to 60mph, with higher gusts, and central pressure has dropped to 994mb.

Tropical Storm Harvey in the western Caribbean Sea.

A very strong burst of convection developed over the center of Harvey during the overnight hours, with cloud tops approaching -85°C, clearly indicating that Harvey is taking advantage of the improved surrounding environment. Strong convection also exists in a cyclonically curved band in the northern semi-circle of Harvey rotating into the developing central dense overcast. Outflow is good to excellent in all but the western quadrant where confluent flow is restricting the expanding high cloud canopy over the Yucatan. Atmospheric moisture is no longer a problem as Harvey's convection has successfully mixed out any remaining dry air.

It is now becoming increasingly likely that Harvey will attain hurricane strength before making landfall between Monkey River Town and Dangriga along the Belize Coast. As mentioned above, conditions are universally conducive for development with high atmospheric moisture content, upper-level high pressure, warm sea-surface temperature around 29°C, and despite the close proximity to land the topography of the region actually fosters development of tropical cyclones. So I'm expecting Harvey to reach 75-80mph, a minimal hurricane and the season's first, before landfall early this afternoon close to the border of the Toledo and Stann Creek districts. After landfall Harvey should quickly begin to weaken and should be downgraded to a depression by early Sunday morning. With strong deep-layer ridging over Texas Harvey shouldn't emerge over the Bay of Campeche and should continue on a westward track into the mountainous terrain where it will dissipate.

Harvey's main impact to the region will be in the form of extremely heavy rainfall over the mountainous terrain of Guatemala. Winds along the coast may cause minimal damage but buildings in the region are built to withstand a minimal hurricane. Storm surge along the coast will be in the 3-5' range so minor beach erosion will be possible but there shouldn't be any damage to the fragile coral reefs offshore.


In the deep tropics there are two disturbances drawing attention at this time. One is about 400 miles east of the Leeward Islands on the Eastern Caribbean and is of most interest at this time. Over the last four days this tropical wave has slowly gained convection but has recently began to tighten its broad low-level cyclonic flow as a tropical depression appears to be in the early stages of formation.

Tropical disturbance '97L'

Currently the tropical wave lies within a region of broad upper-level divergence to the northeast of a fairly weak upper-level low pressure system over northern South America which is aiding in the development of moderate to strong convection along the wave axis and in several cyclonically curved bands feeding into the presumed developing center of circulation. This preliminary fix on this center is 15.5°N, 55.5°W, which appears to be elongated northwest to southeast.

Dry air surrounding the wave has been slowly mixing out as it heads west and shouldn't be any hindrance to further development from this point forward. Sea-surface temperatures are very warm, 0.5 to 1°C above normal, about 28.5 to 29°C, along the future projected path of any cyclonic development and increase to over 30°C from the Bahamas to the Florida Straits right across the Gulf of Mexico. These temperatures are about as warm as it gets in these basins so should development occur there will be plenty of potential heat energy available.

Global models do, in fact, develop this disturbance into a tropical cyclone and take the system across the Greater Antilles from Sunday night through Wednesday morning. During this time development will be a struggle as the system encounters about 10-20kts of southwesterly wind shear due to a lingering upper-level trough through early Tuesday. Proximity to land will also be a problem for intensification so development beyond a storm of tropical storm force doesn't appear likely before Wednesday. Although chances are this system will remain weak as it crosses the islands, rainfall with this system will be particularly intense. The lingering upper trough over the Caribbean will make for increased vertical instability, hence, very strong convection. Also, the forward motion of the system will be less than 10kts so it will have plenty of time to dump flooding rainfall. Where the heaviest rainfall will focus will depend ultimately on the track of any potential cyclone but amounts exceeding 25" in the hardest hit areas is entirely likely. This would lead to severe flooding and mudslides, especially over deforested and destructed Haiti.

After moving past the islands Wednesday night or Thursday the upper-level environment will become very conducive for development as an anti-cyclone develops and establishes itself over the cyclone. As mentioned earlier sea-surface temperatures are very warm in the region of Florida, over 30°C, so a period of rapid intensification could very well occur. There's also indications of this storm growing in size to become a very large entity. With a trough of low pressure in the mid-latitudes moving by to the north the size and vertical structure of the storm will likely govern its future track. A bigger and stronger storm will likely move north faster and possibly take a track up the East Coast. A smaller and weaker storm will likely be less influenced by the passing trough and could turn back towards the west into the Gulf of Mexico. This may all be a moot point should the storm fail to develop but indications are something will develop and will have a major role in the nation's weather this weekend on into early next week.

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Radar: Northeast Region Loop

NE radar
Radar loop of the Northeast region. Courtesy of Weather Underground.

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Local SST's

Northeast SST's
Sea-surface temperatures off the Northeast Coast. Courtesy of NOAA.

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The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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11. originalLT
2:32 AM GMT en Agosto 22, 2011
Thanks for all that "rain" history Sully. Maybe we'll make some more history IF Irene moves up the coast! And this Sunday evening you seem to be right on with your strength projection for Irean too. LT. PS, just got back from FLA. Glad the wedding I had to go to was not schedualed for later this coming week!.
Member Since: Diciembre 31, 1969 Posts: Comments:
10. listenerVT
7:11 PM GMT en Agosto 21, 2011
We are sooo grateful to Crowe1 for his generosity and graciousness, even happily making space for the Ally updates!

Today we had a very nice thunderstorm, which brought heavy rain for a short while. I wish we could have one of these each day, so the gardens would be watered the easy way. :-)

Watching Irene with great interest. I have loved ones along the coast from Florida to Maine.

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9. crowe1
4:29 PM GMT en Agosto 21, 2011
A little one just popped up over me, only .13". Really blowing up to the east of here though. Sunny and nice out now, may have to go for a swim:)
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8. sullivanweather
3:59 PM GMT en Agosto 21, 2011

The vertical structure of the storm is likely to oscillate back and forth for some time. I'm not really expecting the storm to fall apart but I'm not expecting it to rapidly develop either. A slow strengthening to a 70mph tropical storm looks likely before encountering Hispaniola. If this thing rides to the north of Hispaniola without too much effect then I'll start to really worry about something possibly up here; in the Northeast. I'm already resigned to the rain aspect of this storm for our area but should it make a northerly move and only skirt the Southeast Coast and come riding north we could get something to the tune of a Floyd of even bigger.
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7. sullivanweather
3:53 PM GMT en Agosto 21, 2011
Hiya Crowe!

Thanks! It feels good to be back. And look at what follows, a potential tropical system. lol

Getting a nice lil storm here. Popped right over us. Even got some marble-sized hail.
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6. goofyrider
2:42 PM GMT en Agosto 21, 2011
Morn all

Early am 97L was centered near GUADELOUPE and now radar puts it near Nevis. Report the HH found another low level circ. nearer 16.3 N.
Think you were right Sully about apparent trend. If the upper circ is following the westerlies and moving NW-WNW away from the low level we may see a repeat of EM.

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5. crowe1
2:35 PM GMT en Agosto 21, 2011
Hurray!!!!!!!!!!!!!!!!!!!!!!! Sully is back in 'da house!!! Glad to see things are working out for you, we all really missed you. Now worries about the how, what, why, etc. just glad you're back.
I tried to give the "regulars" from your blog somewhere to go but I too was going back to school/new job, blaa, blaa. Plus I have nothing close to your forecasting/analytical skills.
Again, welcome home, we missed you.
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4. sullivanweather
1:20 PM GMT en Agosto 21, 2011

Yesterday was about as good as it gets! Spent my day out in the garden doing a million things. You know how it is out there once it gets toward late summer. Harvesting and trying to beat back the weeds. Tying up plants that want to fall over. Watering because despite all the rain one day of full sun will get those containers.

I'm currently watching the big storms heading this way. Gonna be a really active day today!
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3. listenerVT
6:38 AM GMT en Agosto 21, 2011
Well, Irene is on her way.
There's a chance she'll visit the northeast.
Got supplies?
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2. listenerVT
7:58 PM GMT en Agosto 20, 2011
Thanks Sully! It's amazing any time a tropical storm proceeds according to forecast! Nice!

83º here with sunshine, and the humidity is only 30%~!
Member Since: Diciembre 31, 1969 Posts: Comments:
1. sullivanweather
12:20 PM GMT en Agosto 20, 2011
Hey everyone!

I'll be adding forecasts on 97L and the Northeast as the day progresses. I wanted to get out the latest on Harvey before it makes landfall in a few hours. Thus far everything with Harvey has gone according to forecast.
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