While these phrases can make it sound like the flooding is cyclical, only happening once every 100 or 500 years, it is not. Storms are not on a schedule. Rather, these terms refer to statistical probabilities. For example, the “100-year flood” means there is a 1% chance of a flood of that magnitude happening in any given year in a given location. For the 500-year flood, the probability is 0.2%.
Given the right conditions, it is possible to see multiple 100-year or 500-year flood events in a relatively short period of time.Ellicott City, MD, for example, recently saw two 1000-year flood events only two years apart. For more information, watch the video below from the NWS.
After a relatively mild start to the season, winter’s chill has finally arrived in the northeastern United States. Anarctic outbreak has sent the region into a deep freeze with many cities dealing with the coldest conditions they have seen since last January.
Here in New York City, the mercury fell to 4°F in Central Park on Monday morning and the high only made it to 14°F. While this type of cold shot is not that uncommon in January, it felt rather jarring after the temperature reached the mid-40s the day before.
The city’s normal high for this time of year is 38°F and the normal low is 27°F.
Produced by a deep dip in thejet stream, these current frigid conditions are not expected to last much longer. After a brief warm-up, however, another shot of arctic air is forecast to hit the city next week. So, keep those coats and gloves handy!
When arctic air invades NYC, the Josephine Shaw Lowell Memorial Fountain in Bryant Park often transforms into an icy sculpture. Credit: @nyclovesnyc
The 2018 Atlantic Hurricane Season officially ends today. It marked the third year in a row with above average activity.
According to NOAA, there were fifteen named storms this season. Of these, eight developed into hurricanes and two 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 season was the first since 2008 to have four named storms active at the same time – Florence, Helene, Isaac, and Joyce.
Officially running from June 1 to November 30, the season got off to an early start with Tropical Storm Alberto forming in May. This was the fourth consecutive year to see a pre-season storm develop. The biggest names of the season, however, were Florence and Michael.
In September, Hurricane Florence made landfall in North Carolina and dumped a massive amount of rain on the area. Traveling inland, it caused catastrophic flooding in parts of both North and South Carolina. In Elizabethtown, NC, 35.93 inches of rain was reported, making the wettest tropical cyclone on record for the state. For the contiguous US, it ranked as the eighth wettest.
A few weeks later, Hurricane Michael hit the Florida panhandle as a cat-4 storm. With winds measured up to 155mph, it was the strongest storm on record to strike the region and the third strongest storm to make landfall in the continental US. Its powerful winds and storm surge flooding decimated the Panama City area.
This active hurricane season was largely the result of above-average sea surface temperatures in the Atlantic and ENSO neutral 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.
Overall, the season is reported to have claimed the lives of 154 people and caused an estimated $33 billion in damages. The official tally from NOAA will not be available until early 2019.
Torrential rain events and the flooding they cause are nothing new. Global warming, however, is helping to make them more likely.
Heavy rainfall trends in NYC. Credit: Climate Central
According to the most recentNational Climate Assessment, heavy precipitation events have increased in both frequency and intensity across the United States. While there are seasonal variations with different regions, the greatest increases have been observed in the northeast.
Climate scientists attribute this increase in heavy precipitation to our warming world. As greenhouse gases warm the atmosphere, the air is able to hold more water vapor. More specifically, according to the Clausius–Clapeyron relation, for every increase of 1°F, the saturation level of the atmosphere increases by about 4%. That means there is more evaporation from oceans, rivers, and lakes, and therefore more water vapor available to condense and fall as precipitation.
Heavy rain events have a number of consequences, including an increased risk of both flash floods and river floods. This, in turn, is a threat to life and property. Over the long-term, it also affects insurance rates and property values. According to NOAA, individual billion-dollar flooding events (excluding tropical cyclones) in the U.S. have added up to $39 billion in losses since 2010.
As our global temperature continues to rise, experts say we should expect to see more extreme rain events, even in areas where overall precipitation is projected to decrease. In other words, when it rains, it will likely pour.
Downpours have been getting more frequent and intense across the US. Credit: Climate Central and NCA4
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.)
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.
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.
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.
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.
May was a month of weather extremes is New York City this year. Highs ranged from a cool 53°F to a record warm 92°F. May also produced the city’s first heat wave of the year. However, with 24 out of 31 days posting below average readings, the chill won out in the end. The city’s mean temperature for the month was 61.1°F, which is 1.3°F below average.
In terms of precipitation, May was unusually wet. In all, 6.38 inches of rain were measured in Central Park. Of this impressive total, 3.02 inches (47% of the monthly total) fell in just a few hours on May 5, setting a new rainfall record for the date. Another 1.61 inches came down during an unseasonable nor’easter on May 13. On average, the Big Apple gets 4.19 inches of rain for the entire month of May.
The 2016 Atlantic Hurricane Season officially ends today. Not only was it above average, as predicted, it was the basin’s most active season since 2012.
According to NOAA, there were fifteen named storms this season. Of these, seven developed into hurricanes and three – Gaston, Nicole, and Matthew – 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.
This season’s Accumulated Cyclone Energy (ACE), which measures the intensity and duration of storms, was also above normal. On average, a season will post an ACE of 104 in the Atlantic. This year, according to hurricane researchers at Colorado State University, it was 134.
Officially running from June 1 to November 30, the 2016 season got off to an unusually early start. Hurricane Alex developed in January and made landfall in the Azores. It was the first Atlantic hurricane to occur in January since Hurricane Alice in 1955.
Of the season’s 15 named storms, five made landfall in the US – Bonnie, Colin, Julia, Hermine, and Matthew. Hermine was the first hurricane to make landfall in Florida in 11 years, ending the Sunshine State’s so called “hurricane drought”. The biggest headliner of the season, however, was Hurricane Matthew.
Matthew was the first storm to reach category-5 strength in the Atlantic in nine years. It weakened as it moved northward parallel to the US coast, but unleashed powerful winds and a damaging storm surge in Florida, Georgia, and South Carolina. The storm officially made landfall in South Carolina as a Category-1 hurricane, but its rain bands reached well inland and caused catastrophic river flooding in both North and South Carolina. In Fayetteville, NC – 100 miles from the coast – 14.82 inches of rain was reported.
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.
Despite this busy season, the US has luckily not been hit by a major hurricane since Wilma in 2005. With records dating back to 1851, it is the longest such stretch on NOAA’s books.
According to the latest report from the U.S. Drought Monitor, 49% of the nation is dealing with drought. While this number represents a slight improvement for parts of the west, both the southeast and northeast have been drying out.
Currently, 57% of the southeastern US is in some form of drought and 21% is suffering from conditions of extreme drought. These parched conditions, which have been building for months, are now fueling wildfires across the region. According to the US Forest Service, 59 of the 61 active large wildfires burning in this country are in the southeast.
Another hard hit area is the northeast, where 19% of the region is in severe or extreme drought. Water restrictions are in place in parts of Massachusetts and communities in New Jersey are asking residents to conserve water voluntarily.
On the other side of the country, California – now in its fifth year of drought – received some much-needed rainfall recently. However, most of it fell only in the northern counties. Overall, 88% of the Golden State remains in some form of drought with 21% in exceptional drought, the worst possible category.
The Drought Monitor is a weekly publication produced by a partnership of government agencies, including the National Drought Mitigation Center, the United States Department of Agriculture, and the National Oceanic and Atmospheric Administration.