Kate Forms near Bahamas; Megh Heads toward Yemen Coast after Battering Socotra Island

Kate Forms Near Bahamas; Megh Heads Toward Yemen Coast after Battering Socotra Island

Tropical Storm Kate formed on Monday morning near the Central Bahamas, an unusual occurrence for November during an El Niño year (see below). At 10 am EST Monday, Kate was located about 15 miles east-northeast of Cat Island, moving northwest at 15 mph. The most recent Hurricane Hunter flight confirmed flight-level winds of 50 knots and SFMR surface winds of 40-42 knots, which led NHC to bump up Kate’s top sustained winds slightly to 40 knots (45 mph) in its 10 am advisory. Kate is not the most organized-looking tropical storm, with little evidence of spiral banding and only a ragged cluster of moderately strong convection (showers and thunderstorms) around its small center. Outflow near the top of Kate appears relatively healthy, though.


Figure 1. Enhanced infrared image of Tropical Storm Kate at 1515Z (8:15 am EST) Monday, November 9, 2015. Image credit: NOAA/NESDIS.

Kate should be able to maintain its named status for at least a day or two as it chugs past the Bahamas toward the northwest and north, well off the U.S. East Coast. After a season of relentlessly high wind shear across much of the tropical Atlantic, the shear values are quite low over Kate (5 – 10 knots). Sea surface temperatures near Kate are close to record-warm levels for the time of year: around 28°C (82°F), or 1-2°C above average. Kate is predicted by NHC to strengthen to a 65-mph tropical storm by Wednesday as it recurves to the northwest of Bermuda. Both the statistical SHIPS model and the dynamical HWRF model bring Kate close to the threshold of hurricane strength by Wednesday, with recent runs of the GFDL model even more bullish. Rather than decaying near the end of its life, Kate should then hold its own as a powerful post-tropical cyclone once it gets swept into an upper-level trough moving off the East Coast.

Tropical cyclones in the Atlantic: uncommon during El Niño Novembers
Kate is bucking the tide of El Niño by developing in November. Strong El Niño events typically bring the Atlantic season to an earlier-than-usual close, as the subtropical jet stream gets an increasing boost toward late autumn. If we look at those years since 1950 in which the October-to-December Niño3.4 index was in an El Niño state (at least +0.5°C), only about one in three of those years has produced a named storm in November. Outside of these El Niño years, almost every November since the Atlantic entered an active period in 1995 has seen at least one named storm. The only Atlantic hurricanes observed during El Niño Novembers since 1950 are Ida (2009), Florence and Gordon (1994), the “Perfect Storm” (1991), Frances (1986), and Martha (1969). There have been four years since 1950 with a strong El Niño in play during Oct-Dec (Niño3.4 index of at least +1.5°C). During those four years--1997, 1982, 1972, and 1965--only one named storm managed to develop in November: 1972’s Subtropical Storm Delta, which played out harmlessly far out in the central Atlantic.

Kate is the 11th named system of the 2015 Atlantic hurricane season, just below the 12 named systems observed in an average year from 1970 to 2010. The number of major hurricanes--two, Danny and Joaquin--is also comparable to the long-term average. However, there have only been three hurricanes, less than half of the average total of 6.5. Back in April, the forecast team from Colorado State University called for just 7 named storms, 3 hurricanes, and 1 intense hurricane, with an Accumulated Cyclone Energy (ACE) of 40. The April outlook from private forecasting firm Tropical Storm Risk, Inc., called for 11 named storms, 5 hurricanes, and 2 intense hurricanes, with a predicted ACE of 56. As of this morning, the Atlantic ACE value for 2015 was up to 57, still well below the season-long average of 110. The storm totals observed to date (11 named storms, 3 hurricanes, and 2 major hurricanes) fall within the 70%-likelihood brackets from NOAA’s outlook for the Atlantic season issued in late May.

Tropical Cyclone Megh headed towards a second landfall in Yemen
Tropical Cyclone Megh is threading the needle down the narrow Gulf of Aden in the Arabian Sea, but is weakening due to interaction with land, entrainment of dry air from the nearby deserts, and encounters with cooler patches of water upwelled last week by the passage of Tropical Cyclone Chapala. On Sunday, Megh powered ashore over Yemen's Socotra Island as a major Category 3 storm with 125 mph winds. Although news reports from the area remain sparse, it appears likely that Megh brought a second round of devastation to an island hard-hit the previous week by the passage of Tropical Cyclone Chapala. A BBC report cites AFP as reporting at least two deaths on Socotra due to Megh, with a spokesperson for the Socotra Environment Office reporting more homes destroyed by Megh than by Chapala. The latter cyclone passed just to the north of Socotra Island on November 2 when the storm was at Category 3 strength. Satellite images on Monday morning showed that Megh had suffered significant disruption of its cloud pattern, and by the time the storm reaches the south Yemen coast between Mukalla and Aden sometime on Tuesday, Megh will likely be a rapidly weakening tropical storm. Still, Megh will likely dump heavy rains over a desert region unused to seeing them, and widespread destructive flooding is likely near where the center comes ashore.


Figure 2. MODIS image of Tropical Cyclone Megh in the Gulf of Aden, approaching landfall in western Yemen, at 10:05 UTC November 9, 2015. At the time, Megh was a Category 1 storm with 85 mph winds. Image credit: NASA.


Figure 3. Tropical Cyclone Chapala as seen by the MODIS instrument on November 3, 2015 at 7:20 UTC. At the time, Chapala was making landfall in Yemen as a Category 1 storm with 75 mph winds. Image credit: NASA.

Twin major hurricanes in the Arabian Sea: unprecedented in the historical record
Megh is the second major Category 3 or stronger tropical cyclone to affect Yemen this month. Just a week ago, Tropical Cyclone Chapala took advantage of the the warmest waters ever recorded in the Arabian Sea at this time of year to intensify into a top-end Category 4 storm with 155 mph winds (1-minute average) on October 30, according to the Joint Typhoon Warning Center (JTWC). This made Chapala the second strongest tropical cyclone on record in the Arabian Sea, behind Category 5 Cyclone Gonu of 2007 (165 mph winds). Chapala went on to devastate Yemen's Socotra Island and mainland Yemen near the port city of Mukalla on November 3, killing at least eight people and causing widespread destructive flooding. According to NOAA's Historical Hurricanes tool, prior to this year, there had only been five major Category 3 or stronger tropical cyclones recorded in the Arabian Sea since accurate satellite records began in 1990 (an additional Category 3 storm occurred in 1977.) Thus, two major hurricanes in one month in the Arabian Sea is a remarkable occurrence. Also remarkable is the fact that Megh is the second tropical cyclone to hit Yemen (including Socotra Island) at hurricane strength this month. In the period with good satellite data (1990 – 2014), no tropical cyclones at tropical storm strength hit Yemen, though the nation had been hit by two tropical depressions--Tropical Depression Keila in 2011, and Tropical Depression Three in 2008. That storm was the second costliest natural disaster in Yemeni history, with a $400 million price tag. Longer-term records from 1891 - 2014 show Yemen has been hit by only two tropical storms and no hurricane strength storms; tropical storms hit the coast in May 1959 and May 1960. However, according to Dallas (1891) a tropical cyclone entered the Gulf of Aden in June 1885 and a ship measured 943 mb, making the storm likely to be at least at Category 3 strength (see Membery, 2002, Weather. H/T to Cuban meteorologist Alejandro Adonis Herrera G. for this link.)


Figure 4. Surface analysis of the June 2, 1885 major hurricane in the Gulf of Aden. A ship measured a pressure of 943 mb. Image credit: Membery, Weather, July 2002: "Monsoon tropical cyclones: Part 2."

Air pollution blamed for an increase in strength of Arabian Sea tropical cyclones
The Arabian Sea doesn't get many tropical cyclones since it is small; furthermore, the Southwest Monsoon keeps tropical cyclones from forming much of the year, allowing only a short season from May to early June before the monsoon arrives, and another short season in late October through November after the monsoon has departed. Strong Arabian Sea storms are rare due to high wind shear and copious dry air from the deserts of the Middle East, with just three Category 4 or 5 storms ever recorded--Gonu in 2007, Phet in 2010, and Chapala in 2015. Arabian Sea tropical cyclones during the pre-monsoon period in May and June have become stronger over the past 30 years owing to a reduction in vertical wind shear brought about by dimming of sunlight from air pollution particles primarily emitted in India, said Evan et al. in a 2011 paper published in the journal Nature. The authors did not study how post-monsoon tropical cyclones in October and November, like Tropical Cyclones Chapala and Megh, might be impacted by air pollution. However, the authors did speculate that continued growth in air pollution emissions might also reduce wind shear in the post-monsoon October-November period, and wrote, "In such a case it is plausible that very intense tropical cyclones, which have so far been limited to the pre-monsoon period, could begin to emerge in the post-monsoon season as well."

El Niño matches weekly record from 1997-98
The blockbuster El Niño event of 2015 continues to gather strength in the tropical Pacific. In its weekly update issued on Monday, NOAA reported that the Niño3.4 sea-surface temperature over the past week was 2.8°C above average. This is the highest weekly value reached to date during the current El Niño event, and it matches the peak departure from normal of 2.8°C observed in late November 1997 during the record-setting 1997-98 El Niño. The weekly value could rise a bit more in the next several weeks before leveling off and then slowly dropping through early 2016, as expected from the classic evolution of major El Niño events and in line with indications from forecast models. Even as the Niño3.4 values gradually decline, El Niño’s influence on Northern Hemisphere weather should actually peak during the winter months, as the polar and subtropical jet streams feel the maximum seasonal influence from the El Niño configuration in the tropics. See our Weather Underground El Niño forecast page for much more background on what to expect from this El Niño event, both nationally and globally.



Figure 5. Forecasts issued in mid-October by dynamical and statistical models for the Niño3.4 sea-surface temperature (SST) for nine overlapping 3-month periods. Note that the expected skills of the models, based on historical performance, are not equal to one another. The skills also generally decrease as the lead time increases. Forecasts are typically most accurate from June to December and least accurate from February to May. Differences among the forecasts of the models reflect both differences in model design, and actual uncertainty in the forecast of the possible future SST scenario. Image credit: International Research Institute for Climate and Society/NOAA Climate Prediction Center.


Figure 6. A man dives into Lake Geneva on an unusually warm day in Saint-Prex on Sunday, November 8, 2015, as record-breaking temperatures for the month of November hit Switzerland. Image credit: Fabrice Coffrini/AFP/Getty images.

Heat records tumble over Southeast US, Europe, Japan
November is thumbing its nose at the calendar when it comes to unusually warm temperatures across several parts of the Northern Hemisphere. Much of the Southeast U.S., and especially Florida, have experienced their warmest stretch of weather ever recorded in the first week of November. Uncommon November warmth has also bathed Europe: high temperatures on Sunday ranged from the 60s to near 80°F over much of France and Switzerland, with readings as warm as 30°C (86°F) in parts of Spain and Japan. Stay tuned for details: WU weather historian Christopher Burt is about to dive into the many monthly heat records being established this month in North America, Europe, and Asia, as the planet hurtles toward what is virtually certain to be its warmest year since record keeping began more than a century ago.

Bob Henson and Jeff Masters