TS Colin Becomes Post-Tropical Near the North Carolina Coast

Looking more like a mammoth squall line than a tropical cyclone, former Tropical Storm Colin was reclassified as a post-tropical cyclone at 11 AM EDT Tuesday by the National Hurricane Center (NHC). The ill-defined center of Colin was placed at 34.0°N, 77.0°W, or about 40 miles east-southeast of Wilmington and 40 miles south-southwest of Morehead City. Colin was racing northeastward at 36 mph, a track that will take it well east of North Carolina by Tuesday afternoon. A tropical storm warning remained in effect from Cape Lookout to Oregon Inlet, NC, but will likely be discontinued early Tuesday afternoon. Nearly all of the intense showers and thunderstorms (convection) associated with Colin at midday Tuesday were located along an elongated zone extending from just east of Colin’s center hundreds of miles toward the south. With Colin’s west side so weak, rainfall has been less widespread and intense than earlier expected along the coastline from Georgia to North Carolina.


Figure 1. Infrared satellite image of Tropical Storm Colin at 1415Z (10:15 AM EDT) Tuesday, June 7, 2016. Image credit: NOAA/NESDIS.


Figure 2. A driver's automobile stalls during high tide of Tropical Storm Colin in the Westshore area of Tampa, Fla., Monday, June 6, 2016. Image credit: Octavio Jones/The Tampa Bay Times via AP.

Colin’s impact in Florida
Severe weather associated with Colin’s arrival in Florida was minimal, according to reports compiled by NOAA’s Storm Prediction Center as of Tuesday morning. There were only a handful of reports of high wind and just two tornadoes (one in Duval County in far northeast Florida, and the other a waterspout moving onto the southwest coast near Bonita Beach). Minor coastal flooding was widespread across Florida’s Gulf Coast as winds on the east side of Colin pushed water ashore. A storm surge of just over 4.3 feet was observed at Cedar Key, FL, during low tide around 9 PM EDT Monday. A few hours earlier, the surge was lower, but it combined with one of the largest high tides of the month (as a result of last weekend’s new moon) to create a total storm tide [storm effect + tidal effect] of 5.17 feet. This produced the highest water since 2006’s Tropical Storm Alberto in the low-lying Cedar Key region, flooding a number of businesses and topping the storm tide produced by Tropical Storm Debby in 2012. The juxtaposition of peak storm surge with monthly high tide cycles is both a curse and a blessing, according to storm surge expert Hal Needham: “When surge hits near full or new moon, the peak water level is a bit higher, but the event may be of a shorter duration, as water quickly recedes soon after the high tide.” Colin's water level at high tide came in about 5 inches above Needham’s prediction of 4.72 feet featured in our Monday morning blog post.


Figure 3. Preliminary data show that a storm surge of around 3 feet (red curve minus blue curve) coincided with high tide (blue curve) on Monday afternoon, June 6, 2016, at Cedar Key, FL. The storm surge was even larger during the subsequent low tide. Image credit: NOAA.

Tampa Bay gets a parting blow from Colin
Colin was much less organized than 2012’s Tropical Storm Debby, also a June storm from the eastern Gulf of Mexico. Debby produced a large area of rainfall topping 10” across northern Florida. Even though Colin’s sustained winds at landfall were higher than Debby’s, its rapid northeast motion and marked asymmetry kept the heaviest rains limited to a few localized areas, including the Tampa Bay region. Some of Tampa’s worst weather with Colin arrived with intense rainbands that continued to stream ashore Monday evening into Tuesday morning, long after Colin’s center had moved far to the north. Wind gusts hit 48 mph at Tampa’s Knight Airport just before 1 AM ET. CoCoRaHS reports through 7 AM ET Tuesday showed widespread 5” - 7” rainfall amounts over Pinellas and western Hillsborough Counties, including the Tampa and St. Petersburg areas. The heaviest rains had shifted just south of Tampa by late morning Tuesday. Two other pockets of heavy rain from Colin were in the eastern Florida Panhandle (including a CoCoRaHS report of 8.30” in northern Jefferson County) and in a belt across the far northern Florida peninsula (a whopping 10.95” in far southwest Alachua County).


Figure 4. 24-hour rainfall amounts from 8:00 AM EDT Monday, June 6, 2016, to 8 AM Tuesday, June 7. Image credit: NOAA/NWS Advanced Hydrologic Prediction Service

Named storms during the Atlantic winter: which year do they belong to?
Though it wasn’t a catastrophic event, Tropical Storm Colin made history in one way: Never before have we been tracking the Atlantic’s third named storm of a calendar year this early in the year. There have been just two other “C” storms as early as June since current naming practices began in the 1950s: Hurricane Chris (which began as a named subtropical storm on June 18, 2012) and Tropical Storm Candy (June 23, 1968). Going all the way back to 1851, the previous earliest appearance of the season’s third storm was June 12, 1887, although some early-season storms were undoubtedly missed during the pre-satellite era. What’s more, each of this year’s first three Atlantic named storms have all made landfall: Hurricane Alex in the Azores, Tropical Storm Bonnie in North Carolina, and Tropical Storm Colin in Florida.

It’s a truly impressive achievement to have our third named Atlantic storm of 2016—much less our third landfall—before we’re even halfway through June. But was Hurricane Alex really a 2016 event? One could make a case that extremely early tropical cyclones such as Alex are more closely tied to the previous year’s activity. The seasonality of hurricanes is driven in large part by sea surface temperature, which tends to hit its annual minimum around March in the Northern Hemisphere tropics and subtropics. This would suggest a physical rationale for defining a full-year hurricane season, at least for some research purposes, as running from March through February. In records going back to 1851, four tropical or subtropical cyclones of at least tropical storm strength have developed in January, and a tropical storm nicknamed the Groundhog Day storm developed on February 2, 1952. Then we find a gap until March 6, 1908, when a tropical storm that went on to become an unnamed Category 2 hurricane developed northeast of the Leeward Islands (oddly, this one headed southwest and ended up affecting the islands of Antigua and Basseterre). There is another large gap until the next-earliest tropical storm, Ana, which formed on April 20, 2003.

Based on these records, it could be argued that tropical cyclones in the Atlantic during January and early February, such as Alex, are more closely related to conditions found during the prior June-to-November season than to those that will prevail in the upcoming season. The same notion would apply to Hurricane Pali, which became the Central Pacific’s earliest named storm on record on January 7 of this year. An even more noticeable early-year minimum can be seen in statistics for the Northwest Pacific (see Figure 5 below), with the dip especially prominent because of the large number of tropical cyclones overall in that region. If we lived in the Southern Hemisphere, the calendar-year question would be a no-brainer, since the core of every season straddles two calendar years.

I checked in with Brian McNoldy (University of Miami/RSMAS) for his thoughts on calendar-year climatology. “I think most would agree that Alex was more a late-comer to the 2015 season than an early start to the 2016 season,” McNoldy said. Of course, it could be confusing if some researchers or agencies defined the Atlantic season in a calendar-year fashion while others used a different starting/ending date. “In the end,” McNoldy added, “there are so few extreme cases (Jan-Feb formations) that I doubt it would have any noticeable impact on climatology rankings or calculations.”



Figure 5. Seasonal climatology of tropical storms, typhoons, and super typhoons in the Northwest Pacific for the period 1959 - 2010. Image credit: NOAA/AOML.


Figure 6. Infrared satellite image from 1345Z (9:45 AM EDT) Tuesday, June 7, 2016, showing showers and thunderstorms associated with Tropical Storm Colin (top of image) and TD 1-E (bottom left, along and just off the southern coast of Mexico). Other showers and thunderstorms are associated with a disturbance in the Northwest Caribbean (center of image). Image credit: NASA/MSFC Earth Science Office.

TD 1E is born in the Northeast Pacific, but just barely
NHC began issuing advisories on Tropical Depression 1E, the first of the Northeast Pacific season, on Monday afternoon. TD 1E is associated with the same very broad channel of moisture that extends from the eastern Pacific all the way to Tropical Storm Colin (see Figure 6 above). As with Colin, TD 1E is a quite asymmetric system, with most of its convection concentrated on its east side. Between moderate wind shear and proximity to land, TD 1E is not expected to strengthen before it either dissipates or eases into the south coast of Mexico on Wednesday. Heavy rains and dangerous flash floods and mudslides are possible over the nearby mountainous terrain of southern Mexico and western Guatemala. Farther to the west, a disturbance located some 1400 miles southwest of Cabo San Lucas could undergo some slow development over the next couple of days, posing no threat to land.

Bob Henson