Isaias Packs a Punch

This year marks the fifth anniversary of Hurricane Isaias‘ impact on the Eastern United States.  Isaias was somewhat of a late bloomer of a storm that still managed to pack a punch for the Carolinas and Mid-Atlantic.  Isaias struggled to get its act together as it came up the Eastern Seaboard from the Caribbean and the Bahamas.  The storm finally reorganized within the last six hours before making landfall.  

However, the momentum that Isaias gained before landfall in North Carolina helped it bring quite a wallop in the form of strong winds and even tornadoes as it moved further north in the Mid-Atlantic.  Tracking a more westward track like Tropical Storm David on September 5, 1979, Isaias brought its worst side to Eastern Pennsylvania and the Garden State.  

Isaias Packs a Punch – Storm Facts

Isaias had a brief lifetime.  The storm only lasted for a little more than a week.  Nevertheless, Isaias’ brief journey across the Western Atlantic was a tumultuous one.  After forming on July 28th, Isaias made landfall four times.  The ninth named storm of 2020 was a resilient Category One Hurricane on the Saffir-Simpson Scale.  Isaias endured the rocky terrain of Hispaniola and many struggles after moving through the Bahamas.

Isaias weakened to a tropical storm after its third landfall on Andros Island in the Bahamas.  It took two days before Isaias became a hurricane again around dinner time on August 3rd.   It was a good thing that Isaias had trouble intensifying back to a hurricane.  If there had been more time for the storm to intensify, Isaias could have been much worse for the Carolinas and points further north.

Hurricane Isaias made its final landfall in the southern portion of North Carolina near Ocean Isle Beach late in the evening of August 3, 2020.    Maximum sustained winds were 90 miles per hour.  Minimum pressure had fallen to 986 millibars or 29.12 inches.  The storm was peaking as it was coming ashore.  It had been deepening over the last six hours.

Date and Time	Latitude	Longitude	Max Sustained Winds (mph)	Pressure (mb)
7/28/20 12:00	12.5	-54.0	40	1007
7/28/20 18:00	13.2	-56.4	40	1006
7/29/20 0:00	14.1	-58.3	45	1005
7/29/20 6:00	14.8	-60.3	45	1005
7/29/20 12:00	15.2	-62.2	45	1005
7/29/20 18:00	15.3	-64.0	45	1005
7/30/20 0:00	15.8	-65.7	50	1004
7/30/20 6:00	16.7	-67.2	60	1003
7/30/20 12:00	17.7	-68.5	65	1002
7/30/20 16:15	18.4	-69.3	65	1002
7/30/20 18:00	18.9	-69.8	70	999
7/31/20 0:00	19.9	-71.2	75	996
7/31/20 6:00	20.5	-72.7	80	990
7/31/20 9:00	20.9	-73.4	80	990
7/31/20 12:00	21.3	-74.0	75	992
7/31/20 18:00	22.1	-75.1	80	990
8/1/20 0:00	22.9	-75.9	85	987
8/1/20 6:00	23.6	-76.7	85	987
8/1/20 12:00	24.3	-77.5	80	987
8/1/20 13:00	24.4	-77.7	80	989
8/1/20 18:00	24.8	-78.3	70	993
8/2/20 0:00	25.3	-78.9	70	995
8/2/20 6:00	25.9	-79.2	65	996
8/2/20 12:00	26.6	-79.5	65	995
8/2/20 18:00	27.4	-79.6	70	995
8/3/20 0:00	28.2	-79.7	70	995
8/3/20 6:00	29.1	-79.9	70	995
8/3/20 12:00	30.1	-80.0	70	995
8/3/20 18:00	31.2	-79.7	75	991
8/4/20 0:00	32.8	-79.1	90	986
8/4/20 3:10	33.9	-78.5	90	986
8/4/20 6:00	35.0	-78.1	70	992
8/4/20 12:00	37.7	-76.8	70	993
8/4/20 18:00	40.9	-75.1	65	994
8/5/20 0:00	44.0	-73.1	50	998
8/5/20 6:00	46.7	-71.8	40	1000

From 6:00 PM on August 2nd to an hour before landfall, the pressure in Isaias had dropped 10 millibars.  Ninety percent of that pressure drop occurred in the final six hours before landfall.  As quickly as Isaias had intensified back into a hurricane, it regressed to a tropical storm.  By 6:00 AM on August 8th, Isaias was no longer a hurricane.  Thanks to the convergence of several factors, Isaias maintained tropical storm intensity further north.

The combination of Its forward motion accelerating, baroclinic forcing from a nearby mid-to-upper level trough, and much of its circulation remaining over water, Isaias managed to remain a vigorous tropical storm.  The result was chaotic with plenty of rotation in the atmosphere over the Mid-Atlantic.  According to the final storm report on Isaias by the National Hurricane Center, Isaias generated a combination of heavy rain, damaging winds, and tornadoes in Virginia, Maryland, Delaware, Pennsylvania, and New Jersey.

State	Number of Tornadoes	Strongest on EF Scale and Location
North Carolina	13	EF3 – Woodard in Bertie County
Maryland	10	EF2 – Mardela Springs and Girdletree
Virginia	7	EF2 – Franklin
Delaware	3	EF2 – Suburbs of Dover
New Jersey	2	EF1 – Mamora and Surf City
Pennsylvania	2	EF2 – Northeast Philly Suburbs
Connecticut	1	EF1 – Saugatuck Shores
South Carolina	1	EF0 – Garden City

Isaias spawned 39 twisters from South Carolina and Connecticut.  There were 17 tornado reports in Maryland, Delaware, Pennsylvania, New Jersey, and even Connecticut.  Four of those reports came from Cape May and Ocean County in New Jersey.  The tornadoes spawned by Isaias rank it in the top 20 of all hurricanes in that department.  It was the most tornadoes produced by a landfalling tropical storm or hurricane since Hurricane Florence in 2018.

In the end, Isaias was responsible for 12 deaths across the Caribbean, Carolinas, Mid-Atlantic, and New England.  Ten of those fatalities occurred in the United States.  The storm also resulted in an estimated $4.8 billion in damage in the United States.  Approximately 73 percent or $3.5 billion of the damage was in the Northeastern United States.  It was the costliest tropical system for that part of the country since Superstorm Sandy in October 2012.

Isaias Packs a Punch – Chaos Across the Mid-Atlantic

The morning of August 4, 2020, was a chaotic and stressful one for many residents across the Mid-Atlantic states.  The ability of Isaias to maintain its momentum thanks to much of its circulation over water and moving rapidly up the Eastern Seaboard, the storm generated plenty of rotational thunderstorms.  Greg’s Weather Center and surrounding areas in South Plainfield, NJ took a good beating from the storm.  

During the morning and early afternoon of August 4th, the winds were howling at GWC.  While there was a period of heavy rain, the wind was the most significant feature of this storm at GWC.  The winds were relentless and the most significant since Sandy.  The winds produced loud noises outside Greg’s Weather Center as they ripped across South Plainfield.  Strong winds peaked around midday and downed trees, branches, power lines, and more.  

There was minor damage to the attic at GWC.  Damage was reported as close as a block away from GWC on Ralph Avenue.  More damage occurred in the neighborhoods of Wells Drive and Garden Drive less than a quarter mile from GWC’s location.  Some of this area was blocked off by police. The most significant damage occurred a little more than a mile away on Ceadarbrook Avenue, where there was a downed tree in the front yard of a home.  

GWC captured footage of what appeared to be a funnel cloud, but the rotation was clockwise in nature.  It may explain the damage swath across several neighborhoods nearby.  The path of the anticyclonic funnel moved in a southeast-to-northwest direction from east of GWC.  Further south in the Garden State was even more chaotic.  

Location	Peak Wind Gust (mph)
Smyrna Landing, DE	96
Cape May, NJ	75
Berkeley Twp, NJ	75
Ocean City, NJ	72
Grasonville, MD	71
Toms River, NJ	70
Dewey Beach, DE	68
Lewes, DE	67
Pleasantville, NJ	66
Atlantic City, NJ	66
Perth Amboy, NJ	66
Beach Haven, NJ	65
White Clay Creek, PA	65
Forsythe, NJ	62
McGuire AFB, NJ	62
Wildwood, NJ	62
Dover, DE	60
Hainesport, NJ	60
Waterford Works, NJ	60
Wilmington, DE	59
Millsboro, DE	59
Morristown, NJ	59
Neshanic Station, NJ	59
Rehoboth Beach, DE	58
Georgetown, DE	58
Trenton, NJ	58
Bridgewater, NJ	58
Cecil County, MD	56
Easton Newnam, MD	56
Millville, NJ	56
Monmouth, NJ	56
Bethany Beach, DE	55
Palmer Township, PA	53
Northeast Philadelphia, PA	53
Blackbird Creek, DE	51
Greenwood, DE	51
Readington, NJ	51
Mount Pocono, PA	51
Delmar, DE	50
Fort Washington, PA	50

Two tornadoes were confirmed along the Jersey Shore in Cape May and Ocean counties.  A waterspout developed in Manahawkin Bay off Long Beach Island and became a landspout between Ship Bottom and Brant Beach.  Video footage captured the tornadic storm crossing the Route 72 bridge.  A more fierce twister spun up near Mamora and Strathmere with 100-mile-per-hour winds.

Heading west into Philadelphia, an EF2 tornado whirled across the Northeast Philly Suburbs near Philadelphia Mills Mall in Bucks County at about 10:50 AM.  It was one of five EF2 twisters in the Mid-Atlantic region with 115-mile-per-hour winds.  An EF0 tornado also spun up nearby in Montgomery County.  Moving to the southwest in Delaware, three tornados developed including an EF2 that ravaged the suburbs of the state capital of Dover.

The states of Virginia and Maryland produced nearly half of all the tornadoes from Isaias.  A combined 17 twisters developed across the two states with the strongest being EF2 in intensity on the Enhanced Fujita Scale.  North Carolina had 13 tornadoes itself.  There were an additional 11 reports of damaging winds across the region from Maryland to New Hampshire

High winds downed a tree on an apartment complex in the Northern Mercer County community of Hightstown, NJ.  Numerous trees were reported down from strong winds in Calvert and Anne Arundel counties in Maryland.  There was tree damage in other parts of Eastern Pennsylvania including Lancaster, Pike, and Wayne counties.  In Lancaster County, a tree fell on top of a house near the town of Petersburg.

Looking at the rainfall from Isaias, the amounts ranged anywhere from 2 to 7 inches.  In addition, there were local reports over 8 inches.  GWC received a little less than three-quarters of an inch of rain. Rainfall amounts from Isaias were more significant the further south and west you went in New Jersey.  Heavy rain was reported in Gloucester, Hunterdon, Mercer, Morris, Salem, Somerset, Sussex, and Warren counties.  The most rainfall in the Garden State occurred in Gloucester County with 5.41 inches received in Logan Township.

Closer to GWC, there was a total of 5.03 inches in Long Valley in Morris County.  Bloomsbury in Hunterdon County received 4.18 inches while Bridgewater in Somerset County tallied 3.77 inches of rain.  The most rainfall in the Mid-Atlantic region was in Montgomery County, Pennsylvania, where over eight and a half inches fell in the town of Wynnewood.  Thirty-three locations in Delaware, Maryland, and Pennsylvania reported over 6 inches of rain.  The torrential rainfall resulted in severe flash floods as well as major river flooding.

Location	Rainfall (in inches)
Wynnewood, PA	8.59
Trappe, MD	8.10
Skippack, PA	8.00
Collegeville, PA	8.00
Worcester, PA	7.56
Saint Davids, PA	7.48
Gilbertsville, PA	7.46
Sellersville, PA	7.43
Center Valley, PA	7.25
Grasonville, MD	7.24
Canadensis, PA	7.00
Bossardsville, PA	6.95
Saylorsburg, PA	6.95
Phoenixville, PA	6.75
Smithfield, PA	6.63
Wester Chester, PA	6.61
Villanova, PA	6.61
Easton, MD	6.54
Nazareth, PA	6.54
Coatesville, PA	6.51
Bala Cynwyd	6.43
Kemblesville, MD	6.41
Perryville, MD	6.35
Oxford, PA	6.30
Parkesburg, PA	6.20
Pocono Summit, PA	6.18
Ambler, PA	6.14
New Hanover, PA	6.12
Wilmington, DE	6.10
Norristown, PA	6.08
Royersford, PA	6.07
Upper Macungie, PA	6.06
Swarthmore, PA	6.01

Comparing Isaias to Past Storms in the Mid-Atlantic

For the Mid-Atlantic region, the impact of Isaias was similar to that of what was left of Hurricane David in September 1979.  Both storms took a track to the west of the Garden State.  David’s track was further west since the storm made landfall further south and west along the East Coast in Savannah, Georgia.

The swath of tornadoes in the Mid-Atlantic from David and Isaias are quite comparable.  David, which was a Category Five Hurricane at its peak in the Caribbean, produced 34 tornadoes during its trek up the Eastern Seaboard.  Weakening to a tropical storm, David pummeled the Mid-Atlantic region with the brunt of its wind and tornado impact occurring in Virginia, Maryland, Delaware, and Southeastern Pennsylvania.

Figure 3: Comparing Storm Tracks – Isaias (2020) vs. David (1979) – Courtesy of TroPYcal, HURDAT, and NOAA.

Much of the Garden State received wind damage from David.  I was only at the start of fourth grade at the time, but I can recall how strong the winds were and the numerous tree limbs and branches that were down in the area around GWC at the time.  The storm produced a waterspout in Long Island.  Isaias wasn’t as strong as David was during its lifetime, but it may have had more energy and momentum at the time of landfall.

David had gradually faded as it came ashore in Georgia.  Isaias had deepened quite rapidly to its strongest intensity before landfall.  The latter storm produced a wider swath of strong winds in the Mid-Atlantic.  Isaias’ wind impacts went further into New Jersey while the storm produced more total (39), EF0, and EF1 tornadoes (31).  David generated more powerful twisters with almost twice as many EF2 and EF3 twisters (15) than Isaias (8).