Wednesday, September 9, 2015

Tropical Storm Henri (2015)

Storm Active: September 8-11

On September 7, a low pressure system formed near the tail of a stationary front situated over the central Atlantic, well to the southeast of Bermuda. Despite inhibitive upper-level winds, the system began to produce a concentrated area of shower and thunderstorm activity while it remained nearly stationary. The low became better defined on September 8 and though convection was largely confined to the eastern side of the circulation, it had acquired enough organization that night to be classified Tropical Depression Eight. At the time of its classification, Eight had a large area of maximum winds and some other subtropical characteristics, but was more tropical than subtropical.

Though the satellite presentation remained extremely disorganized, with a broad circulation barely in contact with thunderstorm activity to the east, the system's maximum winds did increase somewhat over the next day and Eight was upgraded to Tropical Storm Henri late on September 9. Soon after, the cyclone began to move northward as the ridge holding it place slowly eroded. It passed well east of Bermuda during the morning of September 10, accelerating toward the north as it did so. Wind shear relaxed later that day, but the poorly organized system, still battling incursions of dry air, was unable to take advantage and remained at minimal tropical storm strength. The circulation became elongated by September 11 with multiple low-level swirls evident on satellite imagery. Henri lost its well-defined center during that afternoon and degenerated into a trough. Its remnants merged with a frontal boundary the next day.

Never in its lifetime did Henri develop any convective structure that circumnavigated the center of circulation. This contributed to its inability to significantly intensify.

Henri (and its progenitor system) remained stationary for a few days due to a ridge to the north before an incoming front allowed it to accelerate poleward.

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