Weather Lingo: Alberta Clipper

The winter season can produce a number of different types of storms. One of these is an Alberta Clipper.

These systems originate in western Canada, on the lee side of the Rocky Mountains. As  Pacific air spills downslope, an area of low pressure develops. From there, it gets caught up in the jet stream and moves to the southeast across the US. Traveling over land, these systems lack a significant source of moisture and generally do not produce much snow- usually around 1 to 3 inches. However, they are known for their strong winds and bitterly cold temperatures.

This type of quick-hitting storm takes its name not only from its place of origin near Alberta, Canada but also from the clipper ships of the 19th century – the fastest ships of the time.

Credit: NOAA

Report Finds Hurricane Harvey’s Record Rainfall Linked to Climate Change

Hurricane Harvey – one of the big names of the 2017 Atlantic hurricane season – unleashed catastrophic flooding in southeast Texas at the end of August. Now, after months of reviewing the data, scientists say the storm was exacerbated by climate change.

According to a peer-reviewed report by World Weather Attribution (WWA), an international coalition of scientists, human-caused climate change made Harvey’s devastating rainfall three times more likely to occur and fifteen percent more intense. Using historical rainfall data and high-resolution climate models to compare conditions in a pre-warming world to those at the time of the storm, the WWA team was able to separate the climate signal from natural variability. They found that the deluge caused by Harvey would have been a 1-in-2400-year event in the absence of global warming, but is now a 1-in-800-year event and becoming more likely.

Heavy rainfall events, in general, are becoming more frequent in many different places, because as the atmosphere warms it can hold more moisture. In fact, it can hold four percent more moisture for every 1°F of warming. This means there is more water vapor available in the air that can fall as precipitation.

After rapidly intensifying in the Gulf of Mexico, Hurricane Harvey made landfall as a category-4 storm in the Texas Coastal Bend region on August 25. It then stalled over the area for several days, unleashing massive amounts of rainfall. Cedar Bayou, outside of Houston, reported a staggering 51.88 inches of rain, setting a new record for the continental US. The storm claimed the lives of 80 people and more than 120,000 residents across the area had to be rescued from their homes. The economic impacts of the deluge are still being tallied, but it is expected to be one of the most expensive in US history.

The WWA study only analyzed the impact of climate change on Harvey’s rainfall, not its role in the storm’s formation or strength.  Those connections remain an active area of research.

Climate change made Hurricane Harvey’s rainfall worse. Credit: Climate Central. (World Weather Attribution is led by Climate Central, a non-profit research group.)

Extremely Active 2017 Atlantic Hurricane Season Comes to a Close

The 2017 Atlantic Hurricane Season officially ends today.  Not only was it above average, as predicted, it was the basin’s fifth most active season on record.

According to NOAA, there were seventeen named storms this season. Of these, ten developed into hurricanes and six were major hurricanes with ratings of category 3 or higher on the Saffir-Simpson Scale. An average season produces twelve named storms, six hurricanes, and three major hurricanes. It is also interesting to note that this year’s ten hurricanes developed consecutively over the course of ten weeks, marking the largest number of hurricanes to form in a row in the satellite era.

This season’s Accumulated Cyclone Energy (ACE), which measures the intensity and duration of storms, was also exceptionally high. On average, a season will post an ACE of 104 in the Atlantic. This year, according to researchers at Colorado State University, it was 226 – the seventh highest in the historical record.

Officially running from June 1 to November 30, the season got off to an early start this year. Tropical Storm Arlene was a rare pre-season storm that developed in April. Another interesting outlier was Hurricane Ophelia in October. It was the easternmost major hurricane ever observed in the Atlantic Basin and the strongest storm on record to hit the Republic of Ireland. The biggest names of the season, however, were Harvey, Irma, and Maria.

In August, Harvey made landfall in Texas as category-4 hurricane. It was the first major hurricane to hit the United States since Wilma in 2005. It was also the wettest storm on record, dumping more than 50 inches of rain in southeastern Texas. This extreme precipitation caused catastrophic flooding in the Houston area.

Hurricane Irma maintained category-5 strength winds for 37 hours before making landfall as a category-4 storm in the Florida Keys. Measuring about 425 miles in diameter, Irma was wider than the Florida peninsula and its effects were felt across the entire Sunshine state in early September.

Just two weeks later, Hurricane Maria devastated Puerto Rico. It was the third category-four hurricane to hit the US, or one of its territories, in less than a month. In 166 years of record keeping, that never happened before.

Causing so much destruction, Harvey, Irma, and Maria will likely be retired from the World Meteorological Organization’s list of storm names.

This active hurricane season was largely the result of above-average sea surface temperatures in the Atlantic and ENSO neutral to cool La Niña conditions in the Pacific. With warm water to fuel storms coupled with reduced wind shear across the Gulf of Mexico, tropical development in the Atlantic basin was essentially unhindered.

In terms of economic impact, ENKI Operations, a private research firm, estimates the property damage, clean up costs, and lost business productivity from this year’s storms to be $206 billion. That would make 2017 the costliest hurricane season on record for the US. The official tally from NOAA will not be available until early 2018.

Data: NOAA

Ex-Hurricane Ophelia Batters Ireland

The remnants of Hurricane Ophelia, the 15th named storm of the 2017 Atlantic Hurricane season, slammed the Republic of Ireland on Monday. It was the strongest storm on record to hit that country.

Ophelia peaked as a category-3 hurricane near the Azores over the weekend, becoming the most intense storm ever observed that far north and east in the Atlantic Basin. Then, it rapidly transitioned to a post-tropical storm that was labeled Ex-Hurricane Ophelia by Met Éireann, Ireland’s national weather service. This means the storm was drawing energy from the difference in air masses rather than the heat and moisture of the ocean.

Despite this technical downgrade, Ophelia still packed a punch. The storm’s powerful winds, which averaged around 57mph, uprooted trees and downed power lines. It also produced significant storm surge flooding along the country’s west coast. Officials say at least three fatalities have been reported and more than 300,000 people are without power.

At Fastnet Rock, off the coast of County Cork, a wind gust of 119mph was reported. If confirmed, it will be the fastest wind gust ever recorded in Ireland.

On the eastern side of the storm, smoke and dust from the wildfires burning in Spain and Portugal were funneled northward over the UK. This caused the sun and sky to appear red in a large part of the region.

It is not unheard of for Europe to be hit by the remnants of a hurricane. However, the storms typically travel west across the Atlantic Ocean in the Trade Winds and then re-curve to the northeast if they do not make landfall in the US, Mexico, or the Caribbean. Ophelia, however, skipped the transatlantic voyage and moved northeast toward Europe after forming southwest of the Azores.

Scientists say the storm’s rapid intensification and unusual track are the result of warmer than normal sea surface temperatures at northern latitudes and a steering current known as the mid-latitude jet stream. This current of air flows from west to east and carried the storm toward Ireland.

As the climate changes and sea surface temperatures continue to warm, the area of the ocean that supports hurricane development will likely expand northward. This will make Europe even more vulnerable to post-tropical storms.

MODIS satellite image of Ex-Hurricane Ophelia over Ireland. Credit: NASA

Hurricane Irma Batters Entire State of Florida

Hurricane Irma, the 9th named storm of this Atlantic Hurricane season, made two landfalls in Florida on Sunday. First, its eye crossed Cudjoe Key, just east of Key West, as a category-4 hurricane. Then, a few hours later,  it came ashore at Marco Island on the state’s Gulf Coast as a category-3 storm.

Measuring about 425 miles in diameter, Irma was wider than the Florida peninsula and its effects were felt across the entire Sunshine state. Powerful winds, heavy rain, and storm surge flooding caused catastrophic property damage in the Keys and along both coasts.

In the west, Naples, FL experienced wind gusts up to 142mph – the strongest recorded during the storm. On the east coast, gusts were clocked up to 109mph in the Miami/Fort Lauderdale area, where three high-rise construction cranes collapsed in the strong winds. The storm surge in both Biscayne Bay and Naples was about four feet above normal tide levels.  In the hard hit Keys, according to FEMA, 25% of homes were completely destroyed and about 65% sustained serious damage.

Reports of toppled trees and downed power lines are widespread. The Department of Homeland Security says 15 million people lost power, making it one of the largest power outages in US history.

Moving north and shifting inland, Irma was downgraded to a tropical storm on Monday. Nevertheless, it continued to pack a powerful punch. Jacksonville, FL reported a record six-foot storm surge and the worst flooding it has seen since Hurricane Dora moved through the area in 1964.

Irma’s wrath was also felt in parts of Georgia and the Carolinas. Along the coast, storm surge flooding inundated communities from Savannah, GA to Charleston, SC. Further inland, the NWS issued its first ever tropical storm warning for the metro-Atlanta area.

Coming just sixteen days after Hurricane Harvey, Irma was the second category-4 storm to make landfall in the US this season. In 166 years of record keeping, never before have two Atlantic hurricanes of such intensity hit this country during the same year.

The death toll from this historic storm currently stands at forty-three, including five fatalities reported in Florida, three in Georgia, and one in South Carolina. The rest are from the Caribbean, where Irma hit multiple islands as a Category 5 storm late last week. Sadly, these numbers are expected to rise as search and rescue efforts continue. The entire region faces a long and expensive road to recovery ahead.

Hurricane Irma makes landfall in southern Florida as a Category-4 storm. Credit: NASA

Hurricane Harvey Hammers Texas

Hurricane Harvey, the eighth named storm of the 2017 Atlantic Hurricane Season, made landfall in Rockport, TX late Friday night. It was the strongest storm to hit the United States in twelve years.

Coming ashore with winds measured up to 130mph, Harvey was classified as a Category-4 hurricane on the Saffir-Simpson Scale. These powerful winds along with storm surge flooding and torrential rain caused catastrophic property damage across the Texas Coastal Bend region. It also downed trees and left hundreds of thousands of people without power. To date, according to local officials, only two storm-related deaths have been reported.

Moving inland, toward Houston, Harvey weakened to a Tropical Storm on Saturday afternoon. However, despite this downgrade in wind speed, its rain bands are still drawing moisture from the Gulf of Mexico and unleashing massive amounts of precipitation. Wedged between two areas of high pressure, the storm is essentially stalled over the region. Therefore, even more flooding rain is expected over the next several days.

Harvey was the first major hurricane – category 3 or higher – to make landfall in the Lone Star State since Hurricane Carla in September 1961.

Satellite imagery from NOAA shows Hurricane Harvey along the Texas Coast. Credit: NOAA

Weather Lingo: The Brown Ocean Effect

Tropical cyclones are fueled by warm ocean water and typically peter out over land. Sometimes, however, their lives are extended by something called the “brown ocean effect”.

This is a phenomenon where a storm derives energy from the evaporation of abundant soil moisture deposited by previous rainfall. Essentially, the saturated soil mimics the role of the ocean allowing a tropical cyclone to maintain its strength or even intensify after making landfall.

For the brown ocean effect to occur, according to a NASA funded study by Theresa Andersen and Marshall Shepherd of the University of Georgia, three criteria need to be met:

  • The soil needs to contain copious amounts of moisture.
  • Atmospheric conditions near the ground must have tropical characteristics with minimal variation in temperature.
  • Evaporation rates must be high enough to provide the storm with sufficient latent heat that it uses for fuel, at least 70 watts averaged per square meter.

Although this process supplies less energy than the ocean, it is enough to sustain a storm for a longer period than normal over land. It was first noticed in 2007 after Tropical Storm Erin made landfall in Texas and then intensified as it traveled inland. It formed an eye over Oklahoma and unleashed a massive amount of rainfall.

Storms that are impacted by the brown ocean effect maintain a warm-core and are known as Inland Tropical Cyclone Maintenance and Intensification events (TCMIs). While rare, they are most common in the US, China, and Australia.

Credit: NBC/TWC

Weather History: Ten Year Anniversary of NYC’s Strongest Tornado

Ten years ago today, an EF2 tornado roared through New York City. It was the strongest twister on record to hit the Big Apple.

NYC Tornado of 2007. Credit: NYT

With winds measured up to 135 mph, it left a trail of destruction nine miles long from Staten Island to Brooklyn with the hardest hit neighborhoods being Bay Ridge and Sunset Park. The storm toppled trees and knocked out power to more than 4,000 customers. It damaged hundreds of cars and dozens of homes, including five that had their roofs ripped off. The storm also dumped 1.91 inches of rain in just one hour, which caused flash floods and the temporary suspension of subway service during the morning commute.

Historically, tornadoes have been rare events in NYC. In recent years, however, they have been happening more frequently. Of the eleven twisters that have touched down in the city since 1950, seven have occurred since 2003.

Note: Tornado ratings moved from the Fujita Scale (F) to the Enhanced Fujita Scale (EF) in 2007.

Tropical Storm Emily Soaks Florida’s Gulf Coast

Tropical Storm Emily, the fifth named storm of the 2017 Atlantic Hurricane Season, made landfall at Anna Maria Island in Tampa Bay, FL on Monday morning. It slammed the Sunshine state’s west coast with heavy rain and winds measured up to 45 mph.

According to the NWS, Valrico, FL, a few miles east of Tampa, saw 8.19 inches of rain. Widespread flooding was reported across the region and Gov. Rick Scott declared a state of emergency for 31 counties.

Most land-falling tropical storms come with a few days warning, as they develop over the ocean before moving toward populated areas. Emily, however, sprung up very quickly. It formed as the result of an out-of season cold front stalling out over the extremely warm waters of the Gulf of Mexico near Florida’s west coast.

Moving across the Florida peninsula, away from the warm waters that fueled it, the storm weakened quickly and was downgraded to a tropical depression. It is forecast to travel northeast out into the Atlantic Ocean. No major impacts are expected along the Eastern Seaboard, but rip currents will be an issue for beachgoers over the next few days from Florida to the Carolinas.

TS Emily moves over central Florida. Credit: NOAA/NASA GOES

Tropical Storm Cindy Batters Gulf Coast

Tropical Storm Cindy, the third named storm of the 2017 Atlantic Hurricane Season, made landfall between Cameron, LA and Port Arthur, TX early Thursday morning. It battered the area with heavy rain and winds measured up to 40 mph.

With rainbands spreading out across the Gulf Coast, flash floods were reported from New Orleans, LA to Pensacola, FL. The storm also downed trees and knocked out power to more than 32,000 customers across six states.

Moving inland, the storm was soon downgraded to a tropical depression. However, it still spawned a destructive tornado in Fairfield, AL. The NWS has given the twister a preliminary rating of EF-2.

The remnants of Cindy are expected to travel northeast over the next several days, unleashing even more torrential rain as it moves along.

Tropical Storm Cindy in the Gulf of Mexico. Credit: NOAA/NWS