Tag Archives: rain

When it Rains, it Pours

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Torrential rain events and the flooding they cause are nothing new.  Global warming, however, is helping to make them more likely.

According to the most recent National Climate Assessment, heavy rain events – defined as the heaviest 1% of all rain events – have become heavier and more frequent across most of the US. The greatest increases have been observed in the northeast, mid-west, and southeast.

Climate scientists attribute this increase in heavy precipitation to our warming atmosphere. Simply put, warm air holds more moisture than cold air. And, the more moisture that builds up in the air, the more rain can fall.

The relentless rain and deadly floods in Texas last month made national headlines, but there are many other examples of similar events in the recent past. In September 2013, Colorado experienced catastrophic flooding caused by overwhelming amounts of rain in a short period of time. Locally, here in the NYC area, the town of Islip on Long Island saw more than 13 inches of rainfall in a single day last August. That equates to 29% of their average annual rainfall. The damage caused by that single event was estimated at $35 million.

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.

The map shows percent increases in the amount of precipitation falling in very heavy events (defined as the heaviest 1% of all daily events) from 1958 to 2012 for each region of the continental United States. These trends are larger than natural variations for the Northeast, Midwest, Puerto Rico, Southeast, Great Plains, and Alaska. The trends are not larger than natural variations for the Southwest, Hawai‘i, and the Northwest. The changes shown in this figure are calculated from the beginning and end points of the trends for 1958 to 2012.

The map shows percent increases in the amount of precipitation falling in very heavy events  from 1958 to 2012 for each region of the continental United States. These trends are larger than natural variations for the Northeast, Midwest, Puerto Rico, Southeast, Great Plains, and Alaska. The trends are not larger than natural variations for the Southwest, Hawai‘i, and the Northwest. Credit: 2014 US National Climate Assessment

NYC Monthly Summary: May 2015

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May was unusually warm and dry in New York City this year.

With 26 out of 31 days posting above average highs, including 18 days with readings in the 80s, May felt more like summer than spring. Overnight lows were also well above average throughout most of the month. All together, the city’s mean temperature for the month was 68.5°F, which is 6.1°F above average.  That makes May 2015 the city’s 3rd warmest May on record.

In terms of precipitation, May was exceptionally dry. Coming on the heels of a parched April, the city, according to the latest report (5/28) from the US Drought Monitor, is currently in a state of moderate drought. All told, the city received a mere 1.86 inches of rain in Central Park. Of this meager total, 1.46 inches fell in a single day – the last day of the month – and caused localized flash floods. May, on average, typically brings NYC 4.19 inches of rain.

Graph Credit: The Weather Gamut

Graph Credit: The Weather Gamut

Graph Credit: The Weather Gamut

Graph Credit: The Weather Gamut

Catastrophic Flooding in Texas

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Relentless rain unleashed catastrophic floods across southeast Texas this past weekend. Coming out of a prolonged drought, officials say this was the worst flooding the region has seen in years.

In Houston, more than 10 inches of rain fell Monday night into Tuesday morning. With the ground already saturated from plentiful spring rains, rivers and bayous swelled out of their banks.  The floodwaters inundated homes, businesses, and major roadways, paralyzing large parts of this country’s 4th largest city.  Rainfall rates reached as high as 4 inches per hour, which prompted the NWS to issue a flash flood emergency – the highest level of flood alert – for the area.  Local officials say 3 people were killed and more than 80,000 people lost power as a result of the flood.

On Sunday, torrential rain in Hays County, TX caused the Blanco River to rise more than 30 feet in 3 hours. Before the river gauge was washed away, it reported a crest of 40.21 feet, which is about 7 feet above the previous record set in 1929. Officials there say the raging water destroyed more than 350 homes and that 13 people are still missing.

Just north of Texas, the Oklahoma City area also experienced severe weather and flooding this holiday weekend. Across both states, floodwaters caused a number of fatalities. The combined death toll currently stands at 14, but is expected to rise.

The intensity of these rain events had two main drivers. First, a mass of warm and deeply saturated air moved north from the Gulf of Mexico.  It then ran into a deep dip in the jet stream, which has been locked in place over the western states recently. This collision triggered intense thunderstorms that wrung tremendous amounts of moisture out of the air.  The result was a series of deadly and destructive deluges across the region.

The Governor of Texas, Greg Abbot, has declared 37 counties from the Red River to the Rio Grande to be disaster areas as a result of recent weather events.  More rain, unfortunately, is forecast for the region this week.

Flooded roadway in Houston. Credit: KTRK

Flooded roadway in Houston. Credit: KTRK

The Wet and Dry Seasons of South Florida

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Seasons are a way of dividing up the year based on changes in weather. The traditional four – winter, spring, summer and fall – are familiar to most people.  In the subtropical climate of south Florida, however, there are really only two – wet and dry. While traveling there recently, I had the chance to learn more about them.

The wet season typically runs from mid-May to November. It produces the vast majority of the region’s average annual rainfall, approximately 60 inches. Temperatures often reach into the 90s and humidity levels are high. With sea-breeze fronts developing along both the Atlantic and Gulf Coasts, thunderstorms can occur almost daily during the summer months.

The dry season runs from December to mid-May. Temperatures at that time of year range from the mid-50s to upper-70s and humidity levels are relatively low. On occasion, continental cold fronts dip down into south Florida, bringing near-freezing temperatures to the region. Any rain associated with these frontal systems tends to sweep through the area quickly. Only about 20% of the region’s average annual rain total falls during the winter months.

South Florida’s largest rainfall totals are usually associated with tropical storms and hurricanes, which are not uncommon between June and November.

Data Source: SERCC

Data Source: SERCC

NYC Monthly Summary: April 2015

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Transitioning to spring, April 2015 felt like a weather rollercoaster in New York City. We had highs that ranged from a chilly 43°F to a balmy 80°F.  In the end, though, the warmth won out. The city’s mean temperature for the month was 54.3°F, which is 1.3°F above normal. That makes April the first month since December to produce an above average temperature in the Big Apple.

In terms of precipitation, April’s famous showers were scarce this year. The city received a mere 2.08 inches of rain in Central Park. Of this meager total, 1.37 inches fell in a single day. On average, NYC typically gets 4.5 inches of rain during the month of April.

Graph Credit: The Weather Gamut

Graph Credit: The Weather Gamut

Climate Change Projections for NYC

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Climate Change is a global problem with impacts that vary from place to place. In New York City, they include hotter temperatures, heavier precipitation events, rising sea levels, and increased flooding. Each one of these local challenges was spelled out in detail by the latest report from the New York City Panel on Climate Change (NPCC).

According to the report, temperatures are expected to increase between 4.1°F and 5.7°F by the 2050s and between 5.3°F and 8.8°F by the 2080s. The frequency of heat waves is forecast to jump from the current average of 2 per year to 6 by the end of century.

Annual precipitation is projected to increase 4% to 11% by the 2050s and 5% to 13% by the 2080s. The report also calls for the number of days with extreme precipitation – heavy rain and snow – to increase 1.5 times by the 2080s.

Local sea levels are expected to rise between 11 inches and 21 inches by the 2050s, 18 inches to 39 inches by the 2080s, and up to six feet by 2100. As an archipelago, NYC is especially vulnerable to sea level rise. Higher sea levels give storm surges a higher starting point, allowing floodwaters to reach further inland. That means Sandy-like flooding will become more probable in the future even with a less powerful storm. In fact, if the high end projections of sea level rise come to fruition, the current 1-in-100 year flood event could happen roughly every 8 years.  The city’s flood zone is expected to double in size by 2100.

These changes are not only significant for their quantities, but also for the rate at which they are forecast to occur.  To put them into perspective, compare them to the recent past. Between 1900 and 2013, the city’s annual temperature increased 3.4°F, mean annual precipitation increased 8 inches, and local sea levels rose by 1.1 feet.

Taking steps to both adapt to and mitigate climate change, NYC has started building flood protection systems and has pledged to reduce its greenhouse gas emissions 80% from 2005 levels by 2050.

Formed in 2008, the NPCC assesses the latest climate science and analyzes the specific impacts facing NYC.  It issues a report every 3 years.

Credit: NPCC 2015 Report

NYC faces an increasing risk of floods due to sea level rise and climate change.                          Credit: NPCC 2015 Report

Drought Update: Late Autumn 2014

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Over the past few weeks, rounds of intense rainstorms fueled by a phenomenon known as a Pineapple Express have soaked the west coast of the United States and helped put a modest dent in California’s nearly 3-year drought.

According to the latest report from the US Drought Monitor, 32% of California is currently facing conditions of “exceptional drought”, the worst possible category. That is an improvement from last week’s 55%.   Nonetheless, 100% of California – a state generally considered to be one the most productive agricultural regions in the world – is still in some form of drought.

Water levels in reservoirs throughout this country’s most populated state also remain low. Lake Shasta and Lake Oroville, the two largest reservoirs in California, are both currently at 33% of total capacity and only 55% of the historical average for the date.

With winter considered the “rainy season” in California, it is possible for additional storms to continue slowly reducing the region’s long-term drought conditions. Scientists working with NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites say that California needs 11 trillion gallons of water, enough to fill more than 16 million olympic-size swimming pools, to completely end the drought.

20141216_CA_trd

Credit: US Drought Monitor

The Five Seasons of the Sonoran Desert

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Seasons are a way of dividing up the year based on changes in weather and daylight hours. Winter, spring, summer, and fall – the traditional four – are familiar to most people. However, while traveling in southern Arizona recently, I had the opportunity to learn about the unusual fifth season of the Sonoran Desert.

The Sonoran desert, covering a large part of the southwestern US and Northern Mexico, basically divides its summer into two parts. “Fore-summer”, occurring in May and June, is very hot and very dry. “Summer monsoon season” follows it from July to mid-September and brings the region soaking rains.  It is considered the major growing season.

Surprisingly lush by desert standards, the Sonoran Desert is one of the wettest deserts in North America.  This is due to the fact that winter there is considered a second rainy season. While the precipitation that falls between December and January is generally not as intense as during the monsoon months, it tends to be more widespread. Overall, the region averages between 3 and 12 inches of rain a year. Spring and Fall are generally warm and dry.

NYC Monthly Summary: October 2014

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October was a bit of weather roller coaster in New York City this year. We had highs ranging from a chilly 53°F to a balmy 77°F. In the end though, with 19 out of 31 days posting warmer than average readings, the warmth won out. All together, the city’s mean temperature for the month was 59.6°F. That is 2.6°F above average.

In terms of precipitation, the city was fairly soggy this October. Central Park measured 5.77 inches of rain, which is 1.37 inches above normal. Most of this came down during three significant rain events that each produced more than an inch of rain in a 24-hour period.  Nonetheless, following a parched August and September, NYC and its surrounding area is still listed as “abnormally dry” on the latest report from US Drought Monitor.

Oct2014_temp

Credit: The Weather Gamut

Oct2014_Rain

Credit: The Weather Gamut

Record Rainfall Floods Long Island

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Record rainfall swamped New York’s Long Island on Wednesday morning. Flash floods prompted evacuations, submerged cars on major roadways, and even uprooted trees. Local officials have also reported one weather-related death.

One of the hardest hit areas was Islip in Suffolk County, where 13.27 inches of rain fell in less than 24 hours. That is more than the town would normally get for an entire summer season and is nearly double its previous daily record of 6.7 inches set in August 1990. The storm also shattered the record for 24-hour rainfall in New York State. The previous record was 11.6 inches, which was measured in Tannersville, NY during Tropical Storm Irene in August 2011.

The intensity of this rain event, according to the NWS, was caused by a few factors. First, several different weather systems came together over Long Island and were fed by moisture from the Atlantic Ocean. Then, the storm essentially stalled in place for hours.

While Suffolk County bore the brunt of the rain, flash flooding also caused problems in nearby sections of New Jersey and Connecticut. Here in New York City, we were mostly unscathed. JFK airport (in Queens) reported 3.2 inches of rain, but less than an inch was measured in Central Park.

Flood waters strand cars on Sunrise Highway in Valley Stream on Long Island, NY. Credit: wpix11

Flood waters strand cars on Sunrise Highway in Valley Stream on Long Island, NY.                 Image Credit: pix11