Irma re-intensified into a Category 3 hurricane at 12:00 UTC on September 3 as it moved southwestwards under the influence of the ridge.
Beginning early the following day, the eye began increasing in size and improving in appearance, while deep convection surrounding the eye became more symmetrical.
Additionally, the hurricane headed into warmer sea surface temperatures as it approached the Leeward Islands.
As a result, Irma underwent another period of rapid intensification, reaching Category 4 intensity at 18:00 UTC on September 4 and Category 5 at 12:00 UTC on September 5.
The extremely powerful hurricane grew in size and became increasingly symmetric, with mesovortices being observed within the well-defined eye, signaling the continued intensification of the storm.
Sustained winds peaked at 180 mph (285 km/h) near 18:00 UTC on September 5 – although it was operationally assessed at 185 mph (295 km/h).
Early on September 6, the storm reached its minimum barometric pressure of 914 mbar (27.0 inHg) just before 06:00 UTC, an estimate based on a dropsonde surface pressure observation and measurements from Barbuda and Saint Barthélemy.
This was the lowest barometric pressure in the Atlantic since Dean in 2007.

Irma made landfall along the northern coast of Barbuda around 05:45 UTC on September 6, at peak intensity; Irma maintained its peak until 12:00 UTC on September 6.
After crossing the island of Barbuda, the hurricane, which maintained its intensity and impressive satellite appearance, struck Saint Martin at 11:15 UTC on September 6 and later Virgin Gorda at 16:30 UTC with winds of 180 mph (285 km/h), though Irma' pressure had risen slightly by the time of its third landfall in Virgin Gorda.
As the hurricane moved away from the Virgin Islands late on September 6, observations from reconnaissance flights indicated that the cyclone weakened and had concentric eyewalls, while a Doppler radar in San Juan, Puerto Rico, also noted a double eyewall.
However, Irma remained a Category 5 hurricane and the wind field expanded.
Late on September 6, the cyclone passed about 60 mi (97 km) north of Puerto Rico.
Moving west-northwestward, Irma closely paralleled the northern coast of Hispaniola throughout the day on September 7.
By late that day however, an eyewall replacement cycle began to take place within the hurricane; reconnaissance aircraft found an elliptical eye later that day, though the wind field continued to expand.
As a consequence of this internal structure change, Irma weakened to a Category 4 hurricane as it passed south of the Turks and Caicos Islands early on September 8.
This subsequently ended the 60-hour contiguous period of Irma maintaining Category 5 intensity, the second longest any Atlantic storm had maintained winds above 156 mph (251 km/h) – only the 1932 Cuba hurricane had lasted for a longer consecutive time period at that intensity, at 78 hours.
Irma re-intensified into a Category 3 hurricane at 12:00 UTC on September 3 as it moved southwestwards under the influence of the ridge. Beginning early the following day, the eye began increasing in size and improving in appearance, while deep convection surrounding the eye became more symmetrical. Additionally, the hurricane headed into warmer sea surface temperatures as it approached the Leeward Islands. As a result, Irma underwent another period of rapid intensification, reaching Category 4 intensity at 18:00 UTC on September 4 and Category 5 at 12:00 UTC on September 5. The extremely powerful hurricane grew in size and became increasingly symmetric, with mesovortices being observed within the well-defined eye, signaling the continued intensification of the storm. Sustained winds peaked at 180 mph (285 km/h) near 18:00 UTC on September 5 – although it was operationally assessed at 185 mph (295 km/h). Early on September 6, the storm reached its minimum barometric pressure of 914 mbar (27.0 inHg) just before 06:00 UTC, an estimate based on a dropsonde surface pressure observation and measurements from Barbuda and Saint Barthélemy. This was the lowest barometric pressure in the Atlantic since Dean in 2007.
Irma made landfall along the northern coast of Barbuda around 05:45 UTC on September 6, at peak intensity; Irma maintained its peak until 12:00 UTC on September 6. After crossing the island of Barbuda, the hurricane, which maintained its intensity and impressive satellite appearance, struck Saint Martin at 11:15 UTC on September 6 and later Virgin Gorda at 16:30 UTC with winds of 180 mph (285 km/h), though Irma' pressure had risen slightly by the time of its third landfall in Virgin Gorda. As the hurricane moved away from the Virgin Islands late on September 6, observations from reconnaissance flights indicated that the cyclone weakened and had concentric eyewalls, while a Doppler radar in San Juan, Puerto Rico, also noted a double eyewall. However, Irma remained a Category 5 hurricane and the wind field expanded. Late on September 6, the cyclone passed about 60 mi (97 km) north of Puerto Rico. Moving west-northwestward, Irma closely paralleled the northern coast of Hispaniola throughout the day on September 7. By late that day however, an eyewall replacement cycle began to take place within the hurricane; reconnaissance aircraft found an elliptical eye later that day, though the wind field continued to expand. As a consequence of this internal structure change, Irma weakened to a Category 4 hurricane as it passed south of the Turks and Caicos Islands early on September 8. This subsequently ended the 60-hour contiguous period of Irma maintaining Category 5 intensity, the second longest any Atlantic storm had maintained winds above 156 mph (251 km/h) – only the 1932 Cuba hurricane had lasted for a longer consecutive time period at that intensity, at 78 hours.
Meteorological history of Hurricane Irma