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The 1935 Labor Day hurricane

Meteorological history
Towards the final 2–3 days of August 1935, the United States Weather Bureau observed conditions favorable for the formation of a tropical cyclone near the Turks Islands. According to the Atlantic hurricane reanalysis project, which finalized their analysis of the storm in 2012, a trough of low pressure organized into a tropical depression within this region northeast of Hispaniola on August 29. The nascent disturbance generally tracked towards the west-northwest during the early part of its history, remaining weak and accompanied by only occasional squalls. On August 31 and into the following morning, the depression moved through The Bahamas and strengthened to a tropical storm, crossing Long Island with winds of 50 mph. At this juncture, the Weather Bureau began issuing advisories on the small tropical cyclone. The storm passed south of Andros Island as it was strengthening into a hurricane on September 1 and began to rapidly intensify thereafter. Contemporaneously, the lack of reported impacts from the storm in The Bahamas obscured the storm's eventual strength. A summary of the storm published by the Weather Bureau in Climatological Data stated that there was "no doubt that the storm was not of hurricane intensity" during the storm's passage of The Bahamas, contrary to modern analyses of the hurricane's history. During the ensuing 24 hours after reaching hurricane intensity, the speed of the hurricane's winds would nearly double, reaching the equivalent of Category 2 intensity on the modern Saffir–Simpson scale by the morning September 2, and Category 5 intensity by nightfall. At around 5 p.m. EST (21:00 UTC) on September 2, the American steamship Dixie recorded a minimum air pressure of 924 mbar (hPa; 27.28 inHg) near the center of the storm, roughly corresponding to the storm exhibiting maximum sustained winds of around 159 mph (256 km/h).

The center of the storm passed over Craig Key at 10 p.m. EST on September 2 (02:00 UTC on September 3) with sustained winds estimated at 185 mph (295 km/h) and a directly measured central pressure of 892 mbar (hPa; 26.34 inHg). Both values were unprecedented in the Atlantic hurricane record – no storm since the beginning of the official Atlantic database had ever attained high winds or low pressures of such magnitudes, and the pressure was at the time the lowest measured in the Western Hemisphere. Other observations of low atmospheric pressures around the time of landfall included 899 mbar (hPa; 26.55 inHg) on Upper Matecumbe Key, 906 mbar (hPa; 26.75 inHg) on Lignumvitae Key, and 914 mbar (hPa; 26.98 inHg) on Long Key. Wind gusts accompanying the storm likely exceeded 200 mph (320 km/h). The hurricane was unusually compact at landfall for its location and intensity: hurricane-force winds spanned only 30 mi in diameter and the radius of maximum wind was only around 6 mi. On Alligator Reef, the air pressure fell 39.28 mbar (1.16 inHg) in 30 minutes as the center passed nearby. The calm of the eye was experienced for 40 minutes at on Lower Matecumbe Key and 55 minutes on Long Key with the night sky visible above. Based on the slow movement of the storm, these periods of calm suggested that the eye spanned about 8 mi across.

After its first landfall, the hurricane emerged into the Gulf of Mexico and paralleled the western coast of Florida while remaining 30 – offshore, recurving from its initial west-northwestward bearing to a northward one. During this period, the hurricane grew in size but gradually diminished in the strength of its winds, dropping below Category 5 intensity on September 3 off Sanibel Island and losing major hurricane status on September 4. Maintaining winds of 100 mph (160 km/h), the hurricane made a final landfall northwest of Cedar Key, Florida at 6 p.m. EST (22:00 UTC) on September 4. Accelerating inland, the cyclone remained at hurricane intensity upon emerging into southern Georgia on September 5 before weakening slightly to a tropical storm later that day. After crossing the Carolinas and Virginia, the cyclone emerged into the Atlantic Ocean with renewed intensity, regaining low-end hurricane strength on September 6 offshore the Delmarva Peninsula. The storm transitioned into a powerful extratropical cyclone the following day while accelerating northeast, producing hurricane-force winds across a wide swath of the North Atlantic. Many ships south of Newfoundland and over the open ocean reported hurricane-force winds between September 7 and September 8. The steamship Black Condor reported a minimum air pressure of 948.9 mbar (hPa; 28.02 inHg) – the lowest pressure measured in connection with the storm outside the tropics – in the vicinity of 51°N, -31°W. On September 10, the storm merged with a larger extratropical cyclone off the coast of southern Greenland.

Record intensity
The Labor Day hurricane made landfall stronger than any other hurricane in the Western Hemisphere and remains the strongest landfalling hurricane in the United States as measured by both maximum winds and central pressure. The observation of a sea-level air pressure of 892 mbar (hPa; 26.34 inHg) remains the lowest ever observed by a ground-based station within a tropical cyclone in the Western Hemisphere. The pressure was measured using an aneroid barometer on a boat in Craig Key, Florida, and scrutinized by the Weather Bureau's Instrument Division laboratory in Washington, D.C., which verified the instrument's veracity: "Records of the lowest pressure were secured from three aneroid barometers, the values ranging from 26.75 to 26.98 inches. [...] One of the barometers, owned by Iver Olson, was shipped to the Weather Bureau in Washington where it was tested in the Instrument Division. Careful laboratory tests showed to be an exceptionally responsive and reliable instrument."

- Ivan Ray Tannehill At the time, the reading was the second lowest measured globally, behind a ship's measurement in a Pacific typhoon in 1927. The Labor Day hurricane was the strongest hurricane recorded in the Atlantic Ocean by central pressure until Hurricane Gilbert in 1988. The storm's maximum winds of 185 mph (295 km/h) were derived from the observed pressure and adjusted for the storm's slow forward motion and small size.

Preparations and forecasts
The first advisory published by the U.S. Weather Bureau on the hurricane, issued at 1 p.m. EST (17:00 UTC) on August 31, assessed that the storm was 60 mi east of Long Island in The Bahamas and advised caution to the southeastern Bahamas and shipping in the vicinity.