Tag Archives: ENSO

Weather Whiplash for NYC

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In any given winter season, a few cold snaps and an occasional warm spell are not that uncommon. This year, however, the temperatures in the northeastern US have been swinging from warm to cold to warm again as if on relentless rollercoaster. This week the region saw another round of this type of weather whiplash, albeit more dramatic than usual.

Here in New York City, the temperature went from a record low of -1°F on Sunday to a high of 54°F on Tuesday. That is a 55° difference in just two days. Our normal high for this time of year is 42°F and our normal low is 29°F.

For the past two winters, multiple extended artic outbreaks courtesy of the polar vortex kept the region colder than average for most of the season. This year, with a strong El Niño in place over the Pacific, warmer than normal conditions have made a strong showing. But, it seems like neither El Niño nor the Polar Vortex has been able to maintain a leading role this winter in the northeast. Rather, they seem to be alternating their appearances leaving us somewhat uncertain as to what will come next.

Dramatic Temperature Swing in NYC this week. Credit: The Weather Gamut

Dramatic Temperature Swing in NYC this week. Credit: The Weather Gamut

NYC Monthly Summary: December 2015

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It was down right balmy in New York City this December! With an average temperature of 50.8°F in Central Park, which is a staggering 13.3°F above average, it was the city’s warmest December on record. The previous record of 44.1°F was set in 2001.

Overall, we had thirty out of thirty-one days with high temperatures above average. Five of those days tied or broke daily high temperature records, including Christmas Eve when the mercury soared to a spring-like 72°F in Central Park. Overnight lows were also above average throughout the month. In fact, this was the first December on record that overnight temperatures did not fall below freezing at least once.

While a few warm days in December is not that uncommon, this extended pattern of sustained warmth was very unusual. Driven primarily by El Niño, a persistent ridge in the jet stream over the eastern US allowed warm southern air to flow further north than it normally would at this time of year.

Given this unseasonable warmth, it is not surprising that only a trace of snow was measured in Central Park this December. On average, NYC usually receives 4.8 inches of snow for the month.  Rain, on the other hand, was plentiful.  In fact, December marked the first time since June that we saw above average rainfall. In all, the city received 4.72 inches of rain, which is 0.72 inches above normal. The majority of this total fell during two separate heavy rain events, which seem to be getting more common. Nonetheless, according to the latest report (12/29) from the US Drought Monitor, the city remains in a moderate drought.

DecTemps

Credit: The Weather Gamut

DecRainfall

Credit: The Weather Gamut

Warmest Christmas on Record for NYC

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It was not a White Christmas in New York City this year, but it was still one to remember as temperatures soared into the record books!

On Christmas Eve, the temperature in Central Park reached a spring-like 72°F. That is a staggering 32°F above average and shattered the old record of 63°F set in 1996. On Christmas Day, the mercury climbed to 66°F surpassing the previous record of 64°F from 1982. The city’s normal high for this time of year is 40°F and the normal low is 29°F.

The primary driver of this unseasonable warmth is El Niño. It has produced a fairly persistent ridge in the jet stream over the eastern part of the country lately that is allowing warm air from the south to flow further north than it normally would in winter.

Talking with both locals and visitors, reactions to this record warmth has been mixed. While some enjoyed being able to walk around without a coat, others said they missed the traditional chill that is associated with the Holiday Season in New York.

Record Warm Christmas Eve 2015, NYC. Photo Credit: Melissa Fleming

Holiday decorations felt out of season this Christmas Eve as temperatures soared to record highs in NYC. Photo Credit: Melissa Fleming

Record-Breaking December Warmth for NYC

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The official start of winter is a week away, but you would never know it in the eastern United States. Temperatures have been so warm that is feels like spring and heat records across the region are being shattered.

Here in New York City, daily high temperature records have been tied or broken for three consecutive days. On Sunday, the temperature reached 67°F in Central Park, breaking the old record of 64°F from 1923. Monday’s high of 67°F tied the record from 1881 and today, in the early morning hours, the mercury climbed to 68°F surpassing the previous record of 67°F from 2008. Evening temperatures have also been exceptionally warm. In fact, the overnight lows have been warmer than the average highs for the past few days. Sunday even posted a new record maximum low of 55°F. The city’s normal high for this time of year is 43°F and the normal low is 32°F.

The primary driver of this unseasonable warmth is El Niño. It has produced a large ridge in the jet stream over the eastern part of the country that is allowing warm air from the south to flow further north than it normally would at this time of year.

To date, according to the NWS, the city is running 12.1°F above average for the month. While this warm weather can be easy to get used to, it makes all the holiday decorations around town feel out of season. So, I guess we can say that El Niño is the Grinch that stole Christmas this year.

WarmDec

NYC is experiencing above average high and low temperatures this December. Credit: The Weather Gamut

May 2015: Warmest May on Record for Planet Earth

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Our global temperature continued to rise last month. In fact, May 2015 was the warmest May ever recorded for the entire planet.

According to a report by NOAA’s National Climatic Data Center, Earth’s combined average temperature for the month – over both land and sea surfaces – was 60.17°F. That is 1.57°F above the 20th century average. The previous record was set last year. NOAA also said the May 2015 global temperature “ties with February 1998 as the fourth highest monthly departure from average for any month on record. The two highest monthly departures from average occurred earlier this year in February and March.”

While heat dominated most of the planet last month, some places were particularly warm. Here in the US, five states – Alaska, Connecticut, Massachusetts, New Hampshire, and Rhode Island – each had a record warm May.

Rising ocean temperatures, according to NOAA, helped fuel the month’s record warmth. The global sea surface temperature for May was 1.30°F above the 20th century average of 61.3°F.  That is the warmest on record for any May surpassing the previous record set just last year. It should be noted, however, that moderate El Niño conditions were present across the central and eastern Pacific Ocean last month.

Year to date, the first five months of 2015 were the warmest of any year on record. Global temperature records date back to 1880.

Credit: NOAA

Credit: NOAA

El Niño is Strengthening and Expected to Last Through Winter

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The current El Niño event, which began in March, is continuing to evolve and strengthen.

According to NOAA, this El Niño has a 90% chance of lasting through the autumn and an 85% chance of sticking around until next winter. While it is more difficult to predict the strength of an El Niño than its duration, the current forecast is calling for a “strong” event, which will likely impact temperature and precipitation patterns around the country.

El Niño is the warm phase of the larger El Niño-Southern Oscillation, known as ENSO. It is a naturally occurring oceanic-atmospheric phenomenon that influences weather around the globe. Its main indicators are warmer than average sea surface temperatures in the eastern and central Pacific Ocean near the equator as well as a weakening of the Trade Winds.

Impacts from a moderate to strong El Niño are usually most noticeable during the autumn and winter months. This is because winter weather is governed more by large scale processes – like nor’easters – than summer weather.  In the US, these impacts include wetter than average conditions from southern California to parts of the east coast and for many of the southern states in-between. Drier than average conditions tend to settle over parts of the Ohio Valley, Great Lakes, and northern Rockies. In terms of temperature, the southwest and southern plains tend to be cooler than average while the northern tier of the country is generally warmer than average.

Although these are considered the typical regional impacts of an El Niño event, they are not guaranteed to happen. Every El Niño is different. It is also important to remember that El Niño is not the only driver of atmospheric circulation. When present, it works in concert with other major players such as daily variability and the influence of climate change.

During the summer months, impacts from El Niño in the US tend to be fairly weak. That said, its presence typically dampens the development of storms during the Atlantic Hurricane Season. As the water in the Pacific warms, it generates convection and creates westerly winds in the upper atmosphere over the Gulf of Mexico, Caribbean Sea, and Western Atlantic. This wind shear tends to limit the strengthening of any tropical cyclones in the area.

Coming on the heels of a record warm 2014, this El Niño event could help push 2015’s average global temperature to even higher record-breaking levels.  Year to date, according to NOAA, the first four months of 2015 have already been the warmest ever recorded.

Typical Winter El Nino

Typical Winter El Niño Pattern for US.  Credit: NOAA

2015 Atlantic Hurricane Season Outlook

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From year to year, the number and strength of storms that develop during the Atlantic hurricane season varies. This year, despite the pre-season arrival of Tropical Storm Ana, NOAA is forecasting a 70% chance of a below average season.

Tropical cyclones, known as hurricanes in the United States, develop around the globe at different times of the year. In this country, we are most affected by the Atlantic hurricane season, which impacts the North Atlantic Ocean, Caribbean Sea and Gulf of Mexico. It runs from June 1 through November 30.

The main driver behind this season’s mild forecast is the presence of El Niño in the tropical Pacific. This naturally occurring oceanic-atmospheric phenomenon is known to impact weather around the planet. According to NOAA, “El Niño can strengthen the trade winds and increase the atmospheric stability across the tropical Atlantic, making it more difficult for cloud systems coming off of Africa to intensify into tropical storms.”

While the overall number of storms expected to develop this year is low, it is important to remember that it only takes one land-falling system to cause serious damage.

Data Source: NOAA

Data Source: NOAA

El Niño has Arrived

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Its official!  NOAA has announced that an El Niño event is underway in the Pacific Ocean. But what, you may wonder, is an El Niño and how will it impact weather in the US?

El Niño is the warm phase of the larger El Niño-Southern Oscillation, known as ENSO. Developing every 3 to 7 years, it is a naturally occurring oceanic-atmospheric coupled phenomenon that influences weather around the globe.

To detect its presence, scientists monitor the Oceanic Niño Index (ONI). This index is based on sea surface temperature anomalies in a rectangular region of the tropical Pacific between 5°N and 5°S latitude and from 120°W to 170°W longitude. When sea surface temperature anomalies in this region exceed +0.5°C, a weak El Nino is present. When they reach +1°C, it is considered a moderate El Niño, and when they go above +1.5°C it is classified as a strong El Niño event.

But warming ocean temperatures are only half the story. There also needs to be a corresponding change in the atmosphere for an El Niño event to be declared. Specifically, there needs to be a weakening of the east-to-west flow of the Trade Winds and a change in tropical rainfall patterns.

Influencing the position of the polar and sub-tropical jet streams, El Niño is most noticeable during autumn and winter. In the US, its impacts typically include wetter than average conditions in California and most of the southern states while drier than average conditions settle across the Ohio Valley, Great Lakes, and northern Rockies. In terms of temperature, the southwest and southern plains tend to be cooler than average while the northern tier of the country is generally warmer than average.

Since every El Niño is different, it is important to remember that none of the regional impacts listed above are guaranteed. We will have to wait and see how this newest El Niño event plays outs.

Credit: Science Island

Credit: Science Island

2014 Atlantic Hurricane Season Outlook

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From year to year, the number and strength of storms developing during the Atlantic hurricane season varies. This year, NOAA’s Storm Prediction Center  is expecting an average to slightly below average season.

Tropical cyclones, known as hurricanes in the United States, develop around the globe at different times of the year. In this country, we are most affected by the Atlantic hurricane season, which impacts the North Atlantic Ocean, Caribbean Sea and Gulf of Mexico. It runs from June 1 through November 30.

The main driver behind this season’s mild forecast is the likely development of El Niño later this summer.  While centered in the tropical Pacific, El Niño impacts weather around the planet. According to NOAA, “El Niño causes stronger wind shear, which reduces the number and intensity of tropical storms and hurricanes. El Niño can also strengthen the trade winds and increase the atmospheric stability across the tropical Atlantic, making it more difficult for cloud systems coming off of Africa to intensify into tropical storms.”

In addition to the seasonal outlook, announced at a press conference in New York City, NOAA also unveiled its new storm surge visualization product. Building on the lessons from super-storm Sandy, this new mapping tool will show the storm surge threat to specific communities beginning when a tropical storm or hurricane watch is issued. Hopefully, this will give the public a better understanding of the dangers of storm surge flooding and allow them to make more informed decisions.

While the overall number of storms expected to develop this year is relatively low, it is important to remember that it only takes one to cause serious damage, if it makes landfall.

Data Source: NOAA

Data Source: NOAA

2013 Atlantic Hurricane Season Forecast

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Hurricane season begins tomorrow and it is expected to be busy.

Tropical cyclones, known as hurricanes in the United States, develop around the globe at different times of the year. In this country, we are most affected by the Atlantic hurricane season, which runs from June 1 through November 30.  Peak activity, however, is usually from August to October when sea-surface temperatures are warmer.

Last year was an extremely active season with nineteen named storms – the third consecutive year with that number.  Four of these made landfall in the US: Beryl, Debby, Isaac, and Sandy.

This year, NOAA is predicting another above average season. Some of the main climate factors of this energetic forecast include warmer than average Atlantic ocean temperatures – which fuel hurricanes – and a currently neutral El Nino-Southern Oscillation pattern in the Pacific.  When the El Nino aspect of this oceanic-atmospheric phenomenon is present, it produces upper level winds that can limit the development of Atlantic cyclones.  The neutral phase of this pattern, however, allows for a more favorable environment for storms to develop.

Atl_Hur_2013Chart Data: NOAA