|Above: Infrared image of Super Cyclonic Storm Kyarr at 18Z (2 pm EDT) Sunday, October 27, 2019. Image credit: CIMSS/SSEC/UW-Madison.|
Spinning west of India, Super Cyclonic Storm Kyarr rocketed to high-end Category 4 strength this weekend, becoming the second strongest tropical cyclone on record in the Arabian Sea behind only Gonu in 2007. As of 12Z Sunday, the Joint Typhoon Warning Center pegged Kyarr’s top winds at 155 mph, just 2 mph shy of Category 5 strength. Kyarr's winds had dropped to 150 mph as of 18Z Sunday, so it may not achieve Cat 5 strength.
Light wind shear (around 5 knots) is one reason Kyarr was able to intensify so quickly. The atmosphere surrounding Kyarr is not especially moist, but sea surface temperatures are unusually warm for this time of year, around 28°C (82°F). SSTs across the Northwest Indian Ocean have been boosted for months by a record-strong positive mode of the Indian Ocean Dipole. A positive IOD typically brings warmer-than-usual water over this region while keeping SSTs toward Indonesia cooler than average, similar to the effects of El Niño and La Niña in shaping SSTs across the equatorial Pacific.
With Cyclone #Kyarr being on the cusp of becoming a category 5 hurricane, it's producing a ton of Accumulated Cyclone Energy (ACE), making this North Indian Ocean hurricane season the most active on record. The ongoing extreme +IOD event probably deserves a lot of blame for this. pic.twitter.com/XjSrb6dt7O— Eric Webb (@webberweather) October 27, 2019
Track models have struggled to agree on Kyarr’s future. Weak steering currents will keep the cyclone’s motion relatively slow. It could eventually head north toward Pakistan, as depicted consistently by the high-resolution HWRF model and more recently by the GFS model. Other track models have tended toward a more westward course, in the direction of Oman. The benefit of Kyarr’s leisurely motion is that it should allow dry air to infiltrate the storm, as wind shear steadily increases this week. JTWC predicted a gradual weakening starting by Tuesday, with Kyarr paralleling the coast of Oman well offshore by Friday.
For more on Kyarr, see the Monday afternoon post from Jeff Masters at Scientific American.
Hurricane Pablo a super-outlier
Against all odds, and expectations, tiny Tropical Storm Pablo became a hurricane on Sunday in the northeast Atlantic after moving through the southeastern Azores. At 11 am EDT, when it was first designated a hurricane, Pablo was centered near 18.3°W and 42.8°N, a latitude further poleward than New York. As of 5 pm EDT, Pablo's top winds had strengthened further, to 80 mph, and the hurricane was now centered at 44.7°N.
Pablo reached hurricane strength in a very unusual location in the North Atlantic basin, arguably more so than Hurricane Vince (2005). This makes Pablo the 2nd northernmost latitude to first reach hurricane intensity in modern records (1950-present). pic.twitter.com/Rz9RjLuc5S— Tomer Burg (@burgwx) October 27, 2019
Like an atmospheric Russian doll, Pablo took shape as a compact warm-core tropical cyclone nested within a much larger non-tropical cyclone. It’s a rare but not unprecedented occurrence. Very cold upper air associated with the upper low gave Pablo the boost it needed. SSTs beneath Pablo’s path, though about 1°C (1.8°F) above average, were only about 18°C (64°F), far below the conventional threshold for tropical development of around 26°C (79°F) and even below the more recently discovered value of 22.5°C (72.5°F) for hybrid/subtropical development. In this case, the frigid air aloft meant that the atmosphere was still relatively unstable, which allowed showers and thunderstorms to form and consolidate around Pablo’s tiny eye (only about 6 to 9 miles in diameter). Other advantages: Pablo’s northeast motion coincided with southwest upper-level flow, thus reducing the impact of otherwise strong wind shear, and twin jet streaks on either side of Pablo helped support upper-level outflow, as noted by Eric Webb.
Pablo’s impact on the Azores appears to have been minimal. The storm passed just southeast of Santa Maria island on Saturday, avoiding landfall and putting the island on its weaker left-hand side. Pablo’s gradual arcing path around the periphery of the upper low will continue, eventually putting the storm atop colder water and into a more stable environment. NHC forecasts Pablo to be a non-tropical cyclone by Monday and to dissipate by Tuesday.
With Pablo’s improbable ascent to hurricane strength, the Atlantic tally for 2019 as of October 27 is 16 named storms, 6 hurricanes, 3 intense hurricanes, and an ACE index of 121.9. The 1981 – 2010 averages for these quantities by October 27 were 10.8 named storms, 5.6 hurricane, 2.5 intense hurricanes, and an ACE index of 95.5, according to Dr. Phil Klotzbach, so 2019 is above average in all metrics.
Out of this year's 16 named storms, just four—Barry, Humberto, Jerry, and Pablo—have peaked in the range between tropical storm and Cat 5 strength, the sign of a highly bifurcated season marked by massively powerful hurricanes together with marginal systems.
Meanwhile, after existing as a tropical storm for a mere six hours, Post-Tropical Cyclone Olga slogged onto the Gulf Coast of southeast Louisiana early Saturday. More than 130,000 people lost power in Louisiana, where wind gusts hit 73 mph at Mandeville north of New Orleans. Several tornadoes struck far south Alabama on Friday afternoon, injuring at least one person. See the weather.com roundup for more on Olga’s impacts.
|Figure 1. Woodbridge firefighter Joe Zurilgen passes a burning home as the Kincade Fire rages in Healdsburg, Calif., on Sunday, Oct 27, 2019. Image credit: AP Photo/Noah Berger.|
Multiple wildfires ripping across California’s parched landscape
A powerful upper-level storm pivoting across California pushed high winds southward across much of the state from Saturday night into Sunday, aggravating an already volatile situation. Wind gusted to 103 mph near Alpine Meadows in the Sierra Nevada, with powerful gusts fanning the Kincade Fire north of San Francisco near Geyserville (more than 30,000 acres burned as of Sunday). Anticipating that the Kicade Fire could be kicked into even higher gear, preemptive evacuation orders were issued on Saturday for much of the North Bay region from Santa Rosa westward to the Pacific—one of the largest such evacuations in memory for the region. Power has been cut by Pacific Gas and Electric to almost 1 million utility customers, possibly affecting several million people, and evacuations have hit more than 185,000 people across Northern California.
The NOAA/NWS Storm Prediction Center has flagged the potential for “extremely critical” fire weather—its highest-concern outlook—for parts of the North Bay on Sunday and for parts of Los Angeles and Ventura counties for Monday. A statewide emergency has been declared by California Governor Gavin Newsom, who announced on Sunday a $75 million program to help state and local governments alleviate the impacts of power shutoffs that have triggered controversy in recent weeks.
Dr. Jeff Masters contributed to this post.