Two Rare January Tropical Storms as seen by RSS Data

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Tuesday, January 26, 2016

The tropics have been more active than normal through the early part of 2016. Hurricane Alex, in the North Atlantic Ocean was the first Atlantic hurricane to form in January since 1938. Alex was a sub-tropical storm on January 13th that quickly intensified to hurricane strength despite sea surface temperatures under 25 °C.  Weak wind shear and a cold upper troposphere may have contributed to Alex's formation. The figure below shows RSS WindSat wind vectors, contoured wind speeds, and rain rates, as well as SSTs derived from the merged microwave SST product during the late morning of January 15th. The areas of no wind data are due to sampling limitations and heavy rain in the area. On January 15th, Alex was asymmetrical in nature, with the strongest winds on the eastern side of the storm.

Another anomalous January tropical storm formed in the Central Pacific.  On January 7th, a tropical depression formed that became Hurricane Pali several days later.  Pali reached hurricane status on January 11th, making it the earliest forming hurricane on record east of the International Dateline.  Pali progressed northward, slowing near 7 °N, 175 °W, and reversing direction. As it meandered southward and began to dissipate, Pali broke another record, becoming the lowest-latitude tropical storm ever in the western hemisphere with its center located near 2 °N. The worldwide record is held by Typhoon Vamei, which in 2001 reached 1.5 °N. 

The cold wake of Pali is obvious in the SST anomaly plot below.  Here, we subtract Reynolds SST climatology data from the RSS Microwave OISSTs on January 12, 2016. These types of plots are visible in the tropical cyclone archive at RSS, available at http://www.remss.com/storm-watch.  The Remote Sensing Systems cyclone archive contains a time series of central pressure, SST, and maximum wind speed, as well as plots of wind vectors and wind speeds, rain rates, and sea surface temperatures from microwave satellite data processed by RSS.  Past images for storms in all basins from 1999-present exist in the archive. 

NASA's Earth Observatory discussed each of these storms in January

 Alex
 Pali