Sam peaked on September 26 as a high-end Category 4 hurricane, with maximum sustained winds of 155 mph (249 km/h) and a minimum central pressure of 927 mbar (27.4 inHg).

The hurricane began to weaken on October 2, as a result of increasing vertical wind shear and cooler sea surface temperatures.

[1] The storm moved east-northeastward to northeastward, and then northward, with increasing forward speed while gradually losing strength, weakening to Category 1 status the following day.

The nascent depression was located in a favorable environment both below and aloft, with sea surface temperatures of 82–84 °F (28–29 °C) and low vertical wind shear.

[10] Intensification was initially slow; the cyclone's center was still attached to the northern edge of a low-pressure trough and the former's surface circulation was only narrowly closed.

[12] The depression was upgraded to Tropical Storm Sam at 15:00 UTC on September 23, after its structure improved significantly on both satellite and microwave imagery; the latter showed a banding feature wrapping around 75 percent of the center.

The combination of a favorable environment, Sam's structural improvement, and the alignment of the cyclone's low- and mid-level centers signaled that rapid intensification was imminent.

The storm continued to track west-northwest, however, its forward speed began to decrease as a result of the mid-level ridge moving to the northwest of Sam.

[17] A small, 12-mi (19-km) wide eye emerged on infrared satellite imagery early on September 25, surrounded by a symmetric ring of cold, −94 °F (−70 °C) cloud tops.

[22] The hurricane continued to intensify through September 26, with the NHC estimating that Sam's peak probably occurred between 19:00 and 22:00 UTC, likely attaining maximum sustained winds of 155 mph (250 km/h) and a minimum central pressure of 927 mbar (27.4 inHg).

[23] Soon after, Sam's eye disappeared entirely from infrared and visible satellite imagery as a result of the replacement cycle and mid-level dry air intrusions from the west.

Upper-level outflow was reduced in Sam's southwestern region as a result of impinging mid-level dry air, and multiple arcus clouds were radiating outward from the western side of the storm.

[34] Shortly after, the cyclone experienced slight weakening as a result of moderate southwesterly wind shear, with Sam's eye becoming cloud-filled and the circulation slanting along the southwest-to-northeast.

[35] Later that day, Sam's overall cloud pattern had improved, however, a Hurricane Hunters reconnaissance aircraft reported that another eyewall replacement cycle was underway.

[39] Early on September 30, Sam began another strengthening trend as the eyewall replacement cycle concluded, located over a warm ocean eddy and within a region of low wind shear.

[42] Sam reached its secondary peak around 09:00 UTC, with maximum sustained winds of 150 mph (240 km/h) and a minimum central pressure of 934 mbar (27.6 inHg).

[55] Sam weakened to a Category 1 hurricane around 21:00 UTC as its cloud tops warmed and its eye vanished from satellite imagery.

[56][57] Sam began to transition to extratropical cyclone shortly after, with its cloud pattern broadening on the northwestern side and convection decreasing.

[62][63] This low then accelerated eastward while rapidly weakening, passing just south of Iceland, before being absorbed by another extratropical cyclone over Scandinavia on October 12.

[64][65][66] While passing northeast of Puerto Rico, light winds associated with Sam's circulation interacted with the typically moist environment and, in conjunction with the normal diurnal cycle, produced locally heavy rainfall on the island on September 28–29.

[70] Although Sam remained more than 900 mi (1,400 km) from the mainland United States, its circulation produced dangerous swells across the Eastern seaboard.