Tropical Storm Rosa (2006)

Tropical Storm Rosa was the first eastern North Pacific tropical storm to develop during the month of November since 2000. The 23rd tropical cyclone and 17th named storm of the 2006 Pacific hurricane season, Rosa developed from a tropical wave that emerged off the west coast of Africa on October 22. The wave traversed the Atlantic Ocean and entered the Pacific Ocean on November 3. Thunderstorm activity began to increase, and it was designated Tropical Depression Nineteen-E on November 8. After fluctuations in organization and intensity, the depression was upgraded to Tropical Storm Rosa on November 9. Persistent wind shear inhibited further intensification, and quickly weakened the storm into a tropical depression on November 10.

Meteorological history
The origins of Rosa are believed to have been from a tropical wave that emerged off the west coast of Africa on October 22, 2006. A weak system, the wave tracked westward and traversed the Atlantic Ocean and Caribbean Sea. No November 3, the wave crossed Central America and entered the eastern North Pacific Ocean. Shower and thunderstorm activity began to increase, and on November 5, a broad low pressure area formed, several hundred miles south of the Gulf of Tehuantepec. Convection gradually became better organized on November 7, and early the next day, thunderstorm activity increased significantly near the center of the low pressure system. At 0600 UTC on November 8, a tropical depression formed about 440 mi to the south of Manzanillo, Mexico.

Located within an area of favorable upper-level winds, the depression started to strengthen. Six hours after formation, satellite imagery suggested the depression was approaching tropical storm intensity. However, later analysis of indicated that the estimated winds may have been inaccurate due to contamination from heavy rainfall. Later on November 8, the storm's convective pattern diminished, and increased wind shear displaced most of the convective activity to the eastern semicircle of the circulation. At the same time, the low-level structure of the cyclone also became disorganized. The conditions were short-lived; by 0000 UTC, a new burst of convection developed and persisted close to the estimated center of circulation. In addition, a banding feature formed in the depression's northeastern quadrant. The storm tracked northwest, as it did throughout its duration, through a weakness in a subtropical ridge. Despite being continually affected by wind shear, the depression was upgraded to Tropical Storm Rosa at around 0600 UTC on November 9. It attained peak winds of 40 mph (65 km/h) at the same time.

The persistent unfavorable wind shear inhibited further intensification, and organization degraded once again shortly after being named. Rosa remained a tropical storm for only 18 hours, becoming a tropical depression at 0000 UTC on November 10. Shortly thereafter, National Hurricane Center forecaster Stewart wrote in Discussion Number 9, "Tropical Depression Rosa is rapidly becoming less organized and may not even be a tropical cyclone any longer. However...just in case another burst of convection fires off near the center...the system is being maintained as a tropical entity for this advisory." The depression degenerated into an open trough later that day.

Records and impact
Tropical Storm Rosa was the first eastern North Pacific tropical storm to develop during the month of November since 2000. It was also the first time a tropical depression formed in November since 2002's Tropical Depression Sixteen-E. Because the storm remained away from land, no effects, property damage or fatalities were reported; no ships were affected, and no tropical cyclone warnings and watches were issued. Due to the lack of any impact, the name Rosa was not retired, and is scheduled to be reused for the 2012 Pacific hurricane season.