A well-organized cluster of thunderstorms with a history of producing widespread damaging winds advanced into a hot, unstable airmass over the Mid Atlantic. This derecho produced widespread, significant wind damage from southern New Jersey southward into the Delmarva during the late evening and overnight of the 29th.
Strong thunderstorm development began across the Midwest and Lower Great Lakes regions during the afternoon of the 29th, with storms initiating across northern Illinois, near Chicago. Strong mid-level winds and an unstable airmass contributed to rapid development as well-organized storms progressed from northern Illinois through Indiana and Ohio. This robust convection continued to track southeastward into an airmass that was even more unstable due to abundant daytime surface heating. Late afternoon temperatures had peaked mainly in the mid to upper 90s with high humidity throughout the Mid Atlantic states, and as the potent thunderstorm cluster progressed from the Great Lakes to the central Appalachians and into the Mid Atlantic by late evening, thunderstorm activity was reinvigorated.
A robust gust front outpaced the main thunderstorm line, producing strong wind gusts as it traveled from the eastern shore of Maryland into Delaware and southern New Jersey. Shortly thereafter, the potent thunderstorm line tracked through the region, with additional damaging wind gusts. One cell in particular around Baltimore, MD experienced rapid intensification and expansion as it raced eastward into northern Delaware and southern New Jersey.  Destructive wind gusts, between 65 mph to nearly 90 mph, were measured as this derecho tracked from the Lower Great Lakes to the Mid Atlantic coast.

Marine Thunderstorm Wind in CP HENLOPEN TO FENWICK IS DE OUT 20NM, ATLANTIC NORTH
From 29-JUN-12 23:30:00 to 30-JUN-12 00:00:00 (EST-5)
Location: LEWES DE
Magnitude: 60.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: WLON

Strong to damaging wind gusts associated with the derecho occurred along the area waters along the entire Sussex County coast.  Measured wind gusts included 60 knots (69 mph) in Dewey Beach and Indian River Inlet.

Marine Thunderstorm Wind in DE BAY WATERS S OF E PT NJ TO SLAUGHTER BEACH DE, ATLANTIC NORTH
From 29-JUN-12 23:30:00 to 30-JUN-12 00:00:00 (EST-5)
Location: EAST POINT NJ
Magnitude: 63.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: WLON

Strong to damaging wind gusts associated with the derecho occurred throughout Delaware Bay. Measured peak wind gusts included 63 knots (72 mph) at Brandywine Shoal Light, 62 knots (71 mph) at the Cape May (NJ) Ferry Terminal and 55 knots (63 mph) in Lewes.

Marine Thunderstorm Wind in DE BAY WATERS N OF E PT NJ TO SLAUGHTER BEACH DE, ATLANTIC NORTH
From 29-JUN-12 23:15:00 to 29-JUN-12 23:50:00 (EST-5)
Location: BOWERS BEACH DE
Magnitude: 63.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: WLON

Strong to damaging wind gusts associated with the derecho passed across all of Delaware Bay. Measured peak wind gusts of 63 knots (72 mph) occurred at Ship John Shoal Light and 58 knots (67 mph) at Bivalve in Cumberland County, New Jersey.

Marine Thunderstorm Wind in LITTLE EGG INLET TO GREAT EGG INLET NJ OUT 20NM, ATLANTIC NORTH
From 30-JUN-12 00:10:00 to 30-JUN-12 00:40:00 (EST-5)
Location: LONGPORT
Magnitude: 67.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: WLON

The derecho produced damaging wind gusts along the entire shore of Atlantic County and claimed the life of a 48-year-old man. The man drowned on Absecon Bay after the 20-foot skiff he was in capsized. The body was recovered at 5 a.m. EDT early that morning. Two other men who were in the boat survived. The capsized vessel washed ashore in a marsh.  Peak wind gusts along marine areas included 67 knots (77 mph) at Point Point, 64 knots (74 mph) in Absecon, 57 knots (66 mph) at the Atlantic City Marina and 56 knots (64 mph) on the Absecon Channel.

Marine Thunderstorm Wind in GREAT EGG INLET TO CP MAY NJ OUT 20NM, ATLANTIC NORTH
From 29-JUN-12 23:40:00 to 30-JUN-12 00:10:00 (EST-5)
Location: CAPE MAY
Magnitude: 49.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: WLON

Strong gusty winds associated with the derecho produced measured wind gusts of 49 knots (57 mph) in Cape May and 44 knots (51 mph) in Ocean City. Comparable wind gusts were estimated by Skywarn Spotters in Sea Isle City and Wildwood.

Marine Thunderstorm Wind in MANASQUAN INLET TO LITTLE EGG INLET NJ OUT 20NM, ATLANTIC NORTH
From 30-JUN-12 00:30:00 to 30-JUN-12 01:00:00 (EST-5)
Location: BEACH HAVEN
Magnitude: 70.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: WLON

Strong to damaging wind gusts associated with the derecho occurred along the area waters east of Ocean County from around Island Beach State Park southward through Little Egg Inlet. The most damaging winds were toward Little Egg Inlet. Winds gusted to 70 knots (81 mph) at Tuckerton, 43 knots (49 mph) at Harvey Cedars and 40 knots (46 mph) at Barnegat Light.