Tropical Storm Karl is developing in the Bay of Campeche and is expected to flood Mexico

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If it seems like Tropical Storm Karl grew virtually overnight, that’s because it did. On Monday, the National Hurricane Center estimated that a disorganized patch of showers and thunderstorms in the southwestern Gulf of Mexico had just a 10% chance of becoming a named storm. Tuesday night was Karl.

Now, tropical storm watches are in effect from Tuxpan to Frontera along Mexico’s east coast, where high winds and torrential rains are expected later in the week. A few rainfall totals could approach a foot, which the National Hurricane Center says could lead to “flare flooding with mudslides in higher ground.”

Rough waves are also expected, with rip currents threatening along beaches in the area. The storm is expected to make landfall between Friday evening and Saturday morning, although gusty showers could start moving ashore Thursday.

While Karl shouldn’t be a problem for the Lower 48, it’s one more name on the World Meteorological Organization’s 2022 list of names for the Atlantic. Despite the recent uptick in activity, the season is still about 20% behind average, defying widespread calls for a busy season.

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To measure overall seasonal hurricane activity, meteorologists rely on a metric known as ACE, or Accumulated Cyclone Energy, which takes into account storm intensity and duration. So far, storms this season have spent 82.2 ACE units on their strong winds, compared to a season-to-date average closer to 103.6 units. ACE is proportional to the square of the wind speed, meaning stronger storms are weighted exponentially more than their weaker counterparts.

About half of this season’s ACE was scorched by just two storms – Ian and Fiona, the latter of which spent around four days as a high-end Category 3 or 4 giant before hitting Nova Scotia. Scotland.

From the point of view of expected number of storms through October 12 based on historical averages, this season is actually very close to normal. At this point, we’ve seen 11 named storms, five hurricanes, and two major hurricanes, compared to averages of 12, five, and two, respectively.

At 10 a.m. central time, Karl was centered about 200 miles north-northeast of Veracruz, Mexico. Karl was crawling north at 3 mph, with maximum sustained winds around 45 mph.

Around 4 a.m. central time, a NOAA buoy northeast of Karl’s center reported sustained winds of 38 mph – just 1 mph from tropical storm strength – and gusting to 42 mph. This builds confidence that sustained winds above the 39 mph threshold are certainly present somewhere in Karl’s inner core.

Tropical storm-force winds extend just over 100 miles from the center of Karl, making it a fairly large storm, although not particularly intense.

On satellite imagery, it appeared that much of Karl’s bad weather was concentrated east of the center. The darker red and white hues on the infrared satellite represent extremely cold, and therefore high, cloud tops.

Karl has almost plateaued in intensity and is expected to remain an unremarkable tropical storm for the next day or so. It will slowly drift west or west-southwest on Wednesday before curving further south-southwest on Thursday.

A possible landing is likely Thursday in Veracruz. Gusty winds to 45 or 50 mph and a light ocean surge, combined with dangerous rip currents, will exist as secondary hazards – the main concern being heavy flooding rain.

The National Hurricane Center predicts a wide 3 to 7 inches, with localized totals of 12 inches in Veracruz and Tabasco.

An unusual training process

Karl was born in a rather roundabout way; it was basically planted by remnant convection, or a bit of pinched thunderstorm activity, from the since disintegrated Julia. Julia made landfall as a Category 1 hurricane in Nicaragua on Sunday, gradually weakening as it skipped the Continental Divide and curved northwest into the Pacific – although its broad storm envelope stretches for hundreds of kilometres.

This group of remnant thunderstorms took on a life of their own, capitalizing on warm ocean waters and flourishing in the wake of favorably weak upper winds. The bowl-like shape of the Bay of Campeche likely enhanced consolidation of vorticity, or rotation, and accelerated Karl formation.

Philippe Papin, a specialist at NOAA’s National Hurricane Center, also noted that a “barrier jet” configuration may have contributed to Karl’s maturation. North-northwesterly winds flowing down the Sierra Madre Mountains helped “close” Karl’s circulation – essentially providing the wind “envelopment” needed to complete a full wind spiral. The generation of a closed low-level center is an integral part of the formation of tropical cyclones; once a near-surface vortex is established, thunderstorm updrafts can stretch it vertically and a tropical storm can quickly assemble around it.

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