On July 23, 2006, about 1653 eastern daylight time, a wheel-equipped Cessna 402B airplane, N991PH, sustained substantial damage when it departed the runway during the landing roll, and collided with a runway sign at the Ft. Lauderdale Executive Airport, Ft. Lauderdale, Florida. The airplane was being operated as a visual flight rules (VFR) cross-country positioning flight under Title 14, CFR Part 91, when the accident occurred. The airplane, registered to Central Florida Therapy Specialists Inc., Eustis, Florida, but operated by the pilot, was returning to Ft. Lauderdale from a company non-revenue flight to the Bimini Islands, Bahamas. The commercial certificated pilot, the sole occupant, was not injured. Instrument meteorological conditions prevailed at the airport at the time of the accident. The flight originated at the South Bimini Airport, Bimini, Bahamas, about 1630, and a VFR flight plan was filed. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on July 27, a Federal Aviation Administration (FAA) inspector, Ft. Lauderdale Flight Standards District Office (FSDO), Ft. Lauderdale, reported that the pilot was returning from South Bimini after dropping off the family of the owner of the airplane. The FAA inspector noted that when used for revenue service, the airplane was operated by Bimini Island Air Inc., Ft. Lauderdale. According to the inspector, the pilot was landing on runway 31 in a thunderstorm, with possible microburst activity. The airplane veered off the runway and collided with a runway sign, and the nose gear collapsed. Following his inspection of the airplane on July 26, the inspector discovered that the propellers struck the ground, and the airplane received structural damage to the fuselage. At 1636, a special weather observation at the Ft. Lauderdale Executive Airport was reporting, in part: Wind, 050 degrees (true) at 10 knots, with gusts to 25 knots; visibility, 1 statute mile in light thunderstorms and rain; clouds and sky condition, 4,600 feet broken, 12,000 feet broken; temperature, 79 degrees F; dew point, 72 degrees F; altimeter, 30.01 inHg. Remarks: peak wind at 1627, 080 degrees at 27 knots; wind shift occurred at 1550. At 1653, an aviation routine weather report (METAR) was reporting, in part: Wind, variable at 6 knots, with gusts to 25 knots; visibility, 1/2 statute mile in heavy thunderstorms and rain; clouds and sky condition, 4,600 feet broken, 12,000 feet broken; temperature, 77 degrees F; dew point, 68 degrees F; altimeter, 30.02 inHg. Remarks: peak wind at 1627, 080 degrees at 27 knots; wind shift occurred at 1550; thunderstorms began at 1613. Neither the pilot nor the company submitted an NTSB Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1).