Relationship between Ocean Temperatures, Shear, and Tropical Cyclones

DISCUSSION: There is no question that as we approach the 2018 tropical Atlantic hurricane season, a primary thought for many millions of people living along the coastlines of the United States is whether they will be impacted the season by a landfalling tropical cyclone.  This is often a very difficult question to answer since it can often be very challenging to pinpoint the exact location of a given landfall at a given time during the tropical Atlantic hurricane season before the season has even gotten underway. Having said that, there are indeed approaches that hurricane forecasters will take from a more fundamental standpoint to better anticipate involving tropical cyclones threats during a given hurricane season.

From a purely fundamental standpoint, it is reasonably well-known across both within and beyond the atmospheric science community that hurricane formation and maintenance chiefly rely upon the presence of both warmer oceanic sea surface temperatures along with weak to moderate vertical wind shear. The reason for this is because the warmer oceanic sea-surface temperatures act as the main source of “fuel” for a developing and/or maturing tropical cyclone.  In addition, the presence of weak to moderate vertical wind shear is also critical since this effectively allows the storm to develop and intensity as opposed to having the critical thunderstorm near the center of the storm be torn apart. This point is reflected by the graphic above which was shared by FEMA Meteorologist Michael Lowry.

Therefore, during periods of time in which there is stronger wind shear present across portions of the tropical Atlantic basin as well as greater vertical wind shear values, this type of dynamic set up is not typically favorable for the development and/or intensification of tropical cyclones.  Hence, when tropical forecasters see either below-normal sea-surface temperatures and/or greater-than-normal magnitudes of vertical wind shear, this is often an initial “red flag” to not anticipate any tropical low-pressure systems which do try to develop to blossom into all-out tropical cyclones.

However, if a given tropical cyclone which tries to develop does happen to both begin its lifetime or move into and then quickly out of a more unfavorable atmospheric environment during the earlier part of its existence, this is a different story. In such situations, if the center of the storm’s circulation does manage to remain out over warm ocean water for a long enough time, then a tropical system may sometimes have the time and ability to further develop into a more formidable tropical cyclone despite being situated in a more hostile environment earlier on in its lifetime.  Hence, it is important during a given hurricane season (regardless of what basin you are concerned about) to never completely write off a given storm even while it is going through a hostile environment since storms can and have been known to “bounce back and surprise.”

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© 2018 Meteorologist Jordan Rabinowitz