In mid-August, a tropical wave emerged off the western coast of Africa.
The northern portion of the wave led to the formation of Tropical Storm Emily in the Atlantic, while the southern portion of the wave continued westward.
It crossed Central America on August 31 and September 1, characterized by a large area of convection and a mid-level circulation.
The disturbance traversed southern Mexico before emerging offshore, where it began to interact with a broad area of low pressure that existed in the eastern Pacific for several days prior.
Shower and thunderstorm activity became concentrated about a well-defined center, leading to the formation of a tropical depression near Manzanillo, Mexico by 12:00 UTC on September 5.
A portion of the tropical wave also combined with monsoonal-like flow across the Bay of Campeche to form Tropical Depression Seven in the Atlantic.

Steered northwest by an anticyclone over northern Mexico and a developing upper-level low west of Southern California, the nascent cyclone steadily organized over warm waters.
A ship about 105 mi (165 km) from the center reported sustained winds of 48 mph (77 km/h), supporting an upgrade to Tropical Storm Greg by 18:00 UTC on September 5.
In spite of dissipating banding features, a large mass of extremely deep convection developed near the center that night.
Radar out of Los Cabos indicated that an eye was in the process of forming by early on September 6, and Greg was upgraded to a Category 1 hurricane in conjunction with satellite intensity estimates by 18:00 UTC that day.
Six hours later, the storm attained its peak intensity with maximum sustained winds of 75 mph (120 km/h) and a minimum barometric pressure of 986 mbar (hPa; 29.12 inHg).
Greg maintained its status for many more hours, even though outflow became restricted to the northeast and low-level cloud lines near the storm's eye became exposed.

A band of convection formed northeast of Greg early on September 7, inducing moderate to strong northeasterly wind shear on the cyclone.
Combined with land interaction, the storm weakened to tropical storm intensity by 18:00 UTC that day, and Greg made landfall near Cabo San Lucas three hours later, with winds of 60 mph (95 km/h).
After turning west-northwest and then west, the cyclone moved over progressively cooler waters and continued to lose strength, although a small area of deep convection persisted.
Greg weakened to a tropical depression by 18:00 UTC on September 8 before succumbing to the unfavorable environment and dissipating a day later west of Baja California Sur.
In mid-August, a tropical wave emerged off the western coast of Africa. The northern portion of the wave led to the formation of Tropical Storm Emily in the Atlantic, while the southern portion of the wave continued westward. It crossed Central America on August 31 and September 1, characterized by a large area of convection and a mid-level circulation. The disturbance traversed southern Mexico before emerging offshore, where it began to interact with a broad area of low pressure that existed in the eastern Pacific for several days prior. Shower and thunderstorm activity became concentrated about a well-defined center, leading to the formation of a tropical depression near Manzanillo, Mexico by 12:00 UTC on September 5. A portion of the tropical wave also combined with monsoonal-like flow across the Bay of Campeche to form Tropical Depression Seven in the Atlantic.
Steered northwest by an anticyclone over northern Mexico and a developing upper-level low west of Southern California, the nascent cyclone steadily organized over warm waters. A ship about 105 mi (165 km) from the center reported sustained winds of 48 mph (77 km/h), supporting an upgrade to Tropical Storm Greg by 18:00 UTC on September 5. In spite of dissipating banding features, a large mass of extremely deep convection developed near the center that night. Radar out of Los Cabos indicated that an eye was in the process of forming by early on September 6, and Greg was upgraded to a Category 1 hurricane in conjunction with satellite intensity estimates by 18:00 UTC that day. Six hours later, the storm attained its peak intensity with maximum sustained winds of 75 mph (120 km/h) and a minimum barometric pressure of 986 mbar (hPa; 29.12 inHg). Greg maintained its status for many more hours, even though outflow became restricted to the northeast and low-level cloud lines near the storm's eye became exposed.
A band of convection formed northeast of Greg early on September 7, inducing moderate to strong northeasterly wind shear on the cyclone. Combined with land interaction, the storm weakened to tropical storm intensity by 18:00 UTC that day, and Greg made landfall near Cabo San Lucas three hours later, with winds of 60 mph (95 km/h). After turning west-northwest and then west, the cyclone moved over progressively cooler waters and continued to lose strength, although a small area of deep convection persisted. Greg weakened to a tropical depression by 18:00 UTC on September 8 before succumbing to the unfavorable environment and dissipating a day later west of Baja California Sur.
Hurricane Greg (1999)