After forming into a hurricane in the central Atlantic on the morning of Friday August 15^th, Hurricane Erin underwent a period of extremely rapid intensification as it was passing northeast of the Leeward Islands, becoming a powerful Category 5 storm and the most rapidly deepening hurricane in the Atlantic before the month of September.  Last year in early October in the then Gulf of Mexico, Hurricane Milton became the fastest Atlantic storm to intensify from a tropical depression to a Category 5 storm. 

Erin originated from an African easterly wave that emerged off the coast of Africa on the 9^th of August.  Soon after passing over the Cape Verde Islands, this wave became focused and strong enough to be named Tropical Storm Erin by the National Hurricane Center (NHC) on the afternoon of August 11^th.  Located well out into the Atlantic about 2300 miles east of the northern Leeward Islands, Erin had plenty of open ocean over which to strengthen.  However, marginal sea surface temperatures that far out into the Atlantic and drier air kept Erin in check, and Erin remained a weak tropical storm as it moved rapidly westward through the central Atlantic.  On the 14^th of August, when it was about 900 miles east of the northern Leeward Islands and sea surface temperatures increasing, Erin began to strengthen, becoming a strong tropical storm with maximum sustained winds reaching 70 mph that evening.

Overnight, NHC reported that Erin had ingested some drier air, keeping the storm in check, but by 11:00 am AST August 15^th, Erin became a hurricane with maximum sustained winds reported at 75 mph.  Erin was now continuing westward about 460 miles east of the northern Leeward Islands. During the day, Erin continued to become better organized with little change in strength, but by later that same evening it began to rapidly intensify with sustained winds reaching 100 mph by 11:00 pm AST.  This rapid intensification continued overnight with pressures continuing to quickly fall and winds increasing to 120 mph by 5:00 am AST.

Download this video from the NASA Scientific Visualization Studio.

It was soon after this time that the GPM Core Observatory overflew Erin.  The following animation provides a detailed look at the structure and precipitation intensity inside Erin at around 10:23 UTC (6:23 a.m. EDT) on August 16^th when Erin was centered about 150 miles northeast of Anguilla.  Surface rainfall estimates from the GPM Microwave Imager (GMI) show areas of moderate (orange areas) to heavy rain (red areas) wrapping around a well-defined eye on the western, southern and eastern sides of the storm. GPM’s Dual-frequency Precipitation Radar (DPR) can also provide a 3D perspective of the precipitation structure within the storm. Areas shaded in bluish gray denote frozen precipitation aloft, while colored areas denote rainfall intensity. The DPR shows several tall convective towers extending above 10 km embedded within the areas of heavier rain, indicating areas of strong thunderstorm activity within Erin.  These result in large amounts of mostly condensational heating being released near the core of the storm and are typically a sign of further strengthening. 

At the time of the GPM overpass, Erin had just become a Category 4 hurricane with NHC reporting the maximum sustained winds at 130 mph.  Erin would go on to become a Category 5 storm at 15:20 UTC (11:20 am EDT) later that same day with sustained winds of 160 mph while passing about 100 miles north of Anguilla in the northern Leeward Islands.

Credits:

Visualization by Alex Kekesi (NASA GSFC / GST) and the NASA Goddard Scientific Visualization Studio using GPM data.

Story by Steve Lang (NASA GSFC / SSAI)