The storms are also causing delays to NJ Transit trains. NJ TRANSIT rail service is subject to up to 60-minute delays system-wide due to downed trees and other storm-related issues, according to NJ Transit. Severe thunderstorms are officially defined as storms that are capable of producing hail that is an inch or larger or wind gusts over 58 mph, according to the National Weather Service. Wind this strong is able to break off large branches, knock over trees or cause structural damage to trees. Some severe thunderstorms can produce hail larger than softballs or winds over 100 mph, so please pay attention to the weather so you know when severe storms are possible. Thunderstorms also produce tornadoes and dangerous lightning; heavy rain can cause flash flooding.