The National Hurricane Center (NHC) began monitoring a tropical wave over western Africa on August 26.
The tropical wave, which was producing a large area of deep convection, moved off the coast of the continent late on August 27.
Throughout the next two days, showers and thunderstorms associated with the wave became better organized and gradually coalesced into a low-pressure area, as the system passed just south of and then through the Cape Verde Islands on August 29; the NHC stated that any significant organization of the disturbance would result in the classification of a tropical depression.
With satellite imagery indicating that a well-defined circulation developed by early on August 30, it was estimated that the system developed into the tenth tropical depression of the season at 00:00 UTC while situated about 140 mi (230 km) west-southwest of São Vicente in the Cape Verde Islands.
Shortly after forming, the banding features associated with the depression increased, and the depression intensified slightly, becoming Tropical Storm Irma at 06:00 UTC.
The NHC operationally began advisories at 15:00 UTC that day, with cyclone already at tropical storm status, based on scatterometer data and satellite estimates.
Strengthening was anticipated due to warm sea surface temperatures and low wind shear, and only slightly cooler waters and drier air were foreseen as a hindrance to intensification.

Moving westward due to a mid-level ridge over the eastern Atlantic, the nascent storm began developing upper-level poleward outflow, as an anticyclone became established over the system, with banding features becoming increasingly evident in satellite images.
Early on August 31, a central dense overcast (CDO) and an eye feature developed, indicating that Irma intensified into a Category 1 hurricane around 06:00 UTC, only 30 hours after tropical cyclogenesis.
The mid-level ridge to the north weakened slightly late on August 31, resulting in the storm curving west-northwestward.
Irma underwent rapid intensification after reaching hurricane status, becoming a Category 2 hurricane at 18:00 UTC and then a Category 3 hurricane, becoming a major hurricane – around 00:00 UTC on September 1.
In a 48-hour period, the hurricane's intensity had increased by 65 mph (105 km/h), a feat achieved only by about 1-in-30 Atlantic tropical cyclones.

On September 2, a ship passed 60 mi (97 km) to the west of the center of Irma, recording maximum winds of 45 mph (72 km/h), while hurricane-force winds were estimated to have extended up to 17 mi (27 km) from the center, both of which indicated that the inner core of Irma remained compact.
After being a major hurricane for about 30 hours, the system weakened slightly to a strong Category 2 hurricane at 12:00 UTC on September 2, likely as a result of drier air and eyewall replacement cycles, with the eye sometimes becoming obscured and the deep convection lining the eyewall appearing weaker.
During this time, Irma began moving west-southwestward under the influence of a strong high pressure area to the north.
The first aircraft reconnaissance flight into the hurricane occurred early on September 4; during the mission, an eye 29 mi (47 km) in diameter and surface winds of 115 mph (185 km/h) were observed.
Although the NHC operationally considered Irma to be a Category 3 hurricane at that time, post-analysis indicated that the storm was still at Category 2 status.
The National Hurricane Center (NHC) began monitoring a tropical wave over western Africa on August 26. The tropical wave, which was producing a large area of deep convection, moved off the coast of the continent late on August 27. Throughout the next two days, showers and thunderstorms associated with the wave became better organized and gradually coalesced into a low-pressure area, as the system passed just south of and then through the Cape Verde Islands on August 29; the NHC stated that any significant organization of the disturbance would result in the classification of a tropical depression. With satellite imagery indicating that a well-defined circulation developed by early on August 30, it was estimated that the system developed into the tenth tropical depression of the season at 00:00 UTC while situated about 140 mi (230 km) west-southwest of São Vicente in the Cape Verde Islands. Shortly after forming, the banding features associated with the depression increased, and the depression intensified slightly, becoming Tropical Storm Irma at 06:00 UTC. The NHC operationally began advisories at 15:00 UTC that day, with cyclone already at tropical storm status, based on scatterometer data and satellite estimates. Strengthening was anticipated due to warm sea surface temperatures and low wind shear, and only slightly cooler waters and drier air were foreseen as a hindrance to intensification.
Moving westward due to a mid-level ridge over the eastern Atlantic, the nascent storm began developing upper-level poleward outflow, as an anticyclone became established over the system, with banding features becoming increasingly evident in satellite images. Early on August 31, a central dense overcast (CDO) and an eye feature developed, indicating that Irma intensified into a Category 1 hurricane around 06:00 UTC, only 30 hours after tropical cyclogenesis. The mid-level ridge to the north weakened slightly late on August 31, resulting in the storm curving west-northwestward. Irma underwent rapid intensification after reaching hurricane status, becoming a Category 2 hurricane at 18:00 UTC and then a Category 3 hurricane, becoming a major hurricane – around 00:00 UTC on September 1. In a 48-hour period, the hurricane's intensity had increased by 65 mph (105 km/h), a feat achieved only by about 1-in-30 Atlantic tropical cyclones.
On September 2, a ship passed 60 mi (97 km) to the west of the center of Irma, recording maximum winds of 45 mph (72 km/h), while hurricane-force winds were estimated to have extended up to 17 mi (27 km) from the center, both of which indicated that the inner core of Irma remained compact. After being a major hurricane for about 30 hours, the system weakened slightly to a strong Category 2 hurricane at 12:00 UTC on September 2, likely as a result of drier air and eyewall replacement cycles, with the eye sometimes becoming obscured and the deep convection lining the eyewall appearing weaker. During this time, Irma began moving west-southwestward under the influence of a strong high pressure area to the north. The first aircraft reconnaissance flight into the hurricane occurred early on September 4; during the mission, an eye 29 mi (47 km) in diameter and surface winds of 115 mph (185 km/h) were observed. Although the NHC operationally considered Irma to be a Category 3 hurricane at that time, post-analysis indicated that the storm was still at Category 2 status.
Meteorological history of Hurricane Irma