What does the 2023 Atlantic hurricane season forecast mean?

The 2023 hurricane season officially begins today, and the experts at NOAA have weighed in with their thoughts on what to expect. The picture is murky, with NOAA predicting almost equal odds of the season being near normal, above normal, or below. 

Graphic courtesy of NOAA

However, NOAA does provide ranges for the number of named storms, hurricanes, and major hurricanes to expect, and all of those numbers are near the long-term average. The numbers are similar to those issued by the team of hurricane season forecasters at Colorado State, who now annually dedicates their forecast in memory of legendary tropical expert Dr Bill Gray. The deterministic CSU forecast is on the low end of NOAA's ranges. Not everyone agrees that this year will feature near or below average tropical development (we see you, UK Met office), but it is the predominant opinion.

The developing El Niño in the equatorial Pacific is expected to play a role in suppressing hurricane development this summer. Since El Niño increases wind shear (especially speed shear) in the critical zone for tropical development in the Caribbean, ENSO positive hurricane seasons tend to have fewer storms. Dry Saharan air and/or dust can impede storm development as well. ENSO's phases can have a downstream impact on trade winds in the Atlantic Ocean, which in turn increases or decreases the wind that blows dust off the Sahara and into the hurricane development zone. 

Impacts of El Niño from June through August.
Graphic courtesy of NOAAClimate.gov

It's important to remember that a seasonal forecast does not provide any insight to the number of storms that will make landfall in a given year. CSU's forecast does offer some guidance on the likelihood of landfall by state, but that forecast is largely based on climatology, not weather. The infographic below shows all the locations where hurricane conditions have been felt on the Atlantic coast since 1950, and it's an example of the type of information CSU uses to create their landfall probability guidance. 

If the above graphic got your wheels turning, here are some noteworthy facts about storms in the Atlantic Basin:

- Statistically speaking, the hurricane season peaks around September 10th. The season officially ends on November 30th, but the number of tropical cyclones rapidly declines after the September 10th peak, and storms can (and do) form in December and beyond. 

- More storms beginning with the letter "I" have had their names retired than any other letter. Since 1954, when the naming convention became official, 13 "I" named storms have been retired. The latest "I" name to be added was 2022's Ian. 

- In the entire 69-year history of named tropical storms, only one name, Allison, was retired without the storm ever reaching hurricane status. Despite the lack of wind, experts decided to retire Allison because of the devastating floods that it caused, especially in the Houston metro area, in 2001.

- Speaking of named storms, in 2021 the WMO ended the practice of using Greek letters for named storms when the alphabetical list is exhausted. Instead, a perennial list of supplemental names will be utilized. The last time we ran out of names on the alphabetical list was in 2020, when a record-breaking 30 tropical storms were named.

- The 2005 season does not hold the record for named storms, but it's the year with the most storm names retired. In addition to Katrina, the deadliest hurricane in US history, the names Dennis, Rita, Stan, and Wilma were also removed from the rolls. 

- On average, the first named storm of the season forms in June, but one of the most notorious hurricanes in American history, Andrew, was the first named storm of 1992. Andrew did not become a Tropical Storm until August 16th, making it one of the latest "first storms" of a single season, and one of only four Category 5 hurricanes to make landfall in the United States. 

MDW forecast calls for lots of sun... and rip currents

Memorial Day weekend marks the start of summer (unofficially speaking) across the country, and locals will undoubtedly pack our beaches and boardwalks for the holiday weekend, especially with such  favorable weather in the forecast. Right now, the ocean is still too chilly for most of us to venture in (the latest reading off the coast of Islip is 57°), but there's an even more serious threat to swimmers and surfers this weekend: rip currents. 

The map below from the local National Weather Service for Philadelphia shows a few tiny, bright blue areas highlighted along the coast of New Jersey and Delaware. Look to the right at the legend, and you'll see that these areas are under a Rip Current Statement. 

Map of weather alerts from the National Weather Service office in Mount Holly, NJ on May 25th, 2023.

A "Rip Current Statement" may not sound serious, but paying attention to it could save your life. In 2021, more than 100 people died as a result of rip currents in the USA. More people died in rip currents than from tornadoes, other wind events, lightning, cold, and winter weather. The blue bars on the chart below show that 2021 was not an anomaly; over a 10-year average, rip currents were the third-biggest weather killer in the United States. 

Weather fatalities in 2021 by type of weather event.
Data and chart from the NCEI Storm Events Database

Rip currents generally don't form due to terrestrial weather. An offshore storm is usually the culprit, and that's the case today as well. The National Hurricane Center is keeping an eye on an area of low pressure off the coast of the Carolinas and Georgia. This area has a small chance of becoming a tropical storm, but it's still intense enough to produce gusty winds, high surf, and the subject of today's blog, rip currents. 

FROM THE NHC: A non-tropical low is expected to form along a front offshore of the southeastern U.S. coast during the next day or two... the system is likely to produce gusty winds and dangerous surf and rip current conditions along portions of the southeastern United States coast late this week and into the weekend.

Rip currents are relatively small, fast-moving areas of water that move away from the shoreline out to sea. They're especially dangerous because they look like calm spots between waves, more inviting than ominous, and they're often fast enough to overpower even the strongest swimmers. 

Photo and caption of a rip current, courtesy of NOAA National Ocean Service

Rip currents are forecast to develop through this weekend due to that offshore low that the NHC is watching. Here's what the Weather Prediction Center thinks the big picture will be tomorrow: 

Forecast surface map for Friday, May 26th from NOAA's WPC

The counterclockwise winds around the low pressure center are capable of pushing ocean water onshore, even hundreds of miles away from the storm's center. The water piles up faster than it can move away. Instead of pushing further onto land, it forms a "rip" back out to sea.

Our coastline here in the Tri-State is especially prone to rip currents. The inward dip created by the coastlines of Long Island and New Jersey make it easier for ocean water to pile in subsequently release in the form of a rip. 

Map of Tri-State, courtesy of EPA.gov

And while NYC's beaches and pools are still in search of more lifeguards, it's especially important to stay vigilant to this common beach hazard. Here are some NOAA resources for identifying rip currents and what to do if you get caught in one. 

Your Tri-State forecast: fire and ice

 If you keep a keen eye on the daily forecast in the Tri-State area, you probably saw at least one of the alerts today, which are depicted in the colorful map below: 

Watches, Warnings, and Advisories valid 12pm ET on May 17th, 2023.

Image from the National Weather Service

Did the top two alerts in the column on the right catch your attention? A Freeze Warning (dark purple) has been issued north of the city for tonight, and a Red Flag Warning (in pink) is in effect for most of the state of Connecticut. In the city, the "Special Weather Statement", shaded in beige, gives information about the potential for fire weather through Wednesday evening. This begs the question: why do we have both fire and ice in the forecast?

First, let's look at the weather setup for today. The image below from NOAA's Weather Prediction Center shows the main weather features in place at 11am ET on Wednesday. The cold front (blue line with triangles) swept through yesterday, bringing barely a drop of rain, is now offshore. In its place, high pressure is nudging in from Quebec, just north of the Great Lakes. 

Surface analysis, valid 15Z on May 17th, 2023.
Image from the WPC

Cold fronts don't always bring cold air; instead, they are marked by a drop in dewpoint after the frontal passage. In simple terms, the air behind a cold front is less humid than the air preceding it. Yesterday's dewpoints were in the upper 40s to low 50s. This afternoon, they are falling into the 20s. The relative humidity has dropped below 30% across much of the Tri-State. Also notice on the map above the isobars, or lines of constant pressure, draped from north to south across New England into the Tri-State. Those lines indicate winds from the north, bringing in drier continental air from Canada. The lines are also fairly close together in relation to the other isobars on the map. This reflects the gusty breezes we've seen today, which have topped 30mph at times. The National Weather Service issued a Red Flag Warning in Connecticut because of this combination of dry air and gusty winds. 

Fire weather is not as common in May as it is earlier in the spring because as new growth develops on our trees and shrubs, it introduces moisture into the air (the process is called transpiration). In mid-May, this process is usually robust enough to keep humidity a little higher at ground level. But it hasn't rained in the Tri-State in about 10 days, and surface water is in short supply. You may have even noticed that there wasn't much dew on the grass this morning; dewy grass is usually the most obvious sign of transpiration. The newly-sprouted leaves also provide a canopy to shade the forest floor from the strongest rays of the sun. If any wildfires do happen today, they will most likely happen in spots that are not shaded.

Wildfires start more readily when a canopy of trees is not present.

Image courtesy of Drought.gov

As it turns out, the same weather setup that produces today's elevated fire danger is also responsible for the Freeze Warning in tonight's forecast. Temperatures could drop into the 20s north and northwest of the city, despite high temperatures in the 60s across most of the area. Dry air heats and cools more readily than humid air, so once the sun sets this evening, the heat that accumulated during the day will quickly escape into the upper atmosphere. Windy conditions can help impede the cooling process by keeping the atmosphere "mixed"; that is, not allowing for a sharp vertical temperature difference. However, our winds are expected to settle down after sunset as the center of high pressure slides closer to the Tri-State, allowing temperatures to drop as much as 30° or greater overnight. The cooldown will be especially pronounced inland, away from the tempering influence of the Atlantic Ocean, and at higher elevations, where the air is less dense and even more susceptible to nighttime heat loss. 

USDA plant zone hardiness map. Farmers and gardeners use their hardiness zone as guidance for planting and harvesting.
Image available for download at usda.gov

As you may know, Frost and Freeze alerts are only issued during the growing season; that's why we don't see these warnings in the winter. For more information on your growing zone, and how it has shifted in recent decades, check out this research by Climate Central. 

Thanks for nothing, El Niño! Drought relief in the southern Plains not likely

NOAA issued its weekly drought report today, and the news continues to be bad for the southern Plains, especially west Texas, Oklahoma, Kansas, and Nebraska. On the map below, the areas shaded in deep red are suffering the worst drought conditions, which are referred to as "exceptional":

Drought monitor from May 9th, 2023.
Produced by the National Drought Mitigation Center and University of Nebraska, Lincoln

Unfortunately, the Climate Prediction Center is holding out little hope that the situation will improve in the coming weeks and months. Below is the seasonal drought outlook until the end of July. Notice that roughly the same areas are expected to remain at least in severe drought: 

 

US Seasonal Drought Outlook, valid May 1 - July 31, 2023.

Courtesy NOAA Climate Prediction Center

The CPC forecast for precipitation reinforces the notion that it's going to remain dry in the region. 

Seasonal Precipitation Outlook for the CONUS & Alaska, valid May - July, 2023.

Courtesy NOAA Climate Prediction Center

The forecasted return of El Niño has its fingerprints on this forecast. As mentioned here, ENSO's impacts are much more significant in the winter than in the summer, especially in the continental US. But, there's still something to be taken from a forecast of ENSO-positive conditions taking hold this summer. The main takeaway is the strength and position of the storm track. 

Depiction of the Pacific Jet Stream during ENSO phases.
Courtesy of NOAA National Weather Service

As you can see in the image above, El Niño conditions generally strengthen the southern branch of the jet stream and make it flatter (yellow line), with less pronounced dips and ridges. During the summer months, the jet is usually at its weakest, because jet stream winds are derived from a temperature contrast between the equator and the poles. As you might expect, this gradient gets weaker in the summer, when the sun's direct rays are in the Northern Hemisphere. But El Niño enhances the southern jet, leading to a more active storm track and more chances for precipitation. Here's the precip outlook map again so you don't have to scroll up:

This could be one of the reasons the CPC anticipates more precipitation (green blob) from the Ohio River valley to Florida. But what's behind the brown shading from Arizona to the Texas panhandle? Isn't this region also the southern US? Alas, the double-edged sword of El Niño may be to blame. At the same time El Niño strengthens the southern jet, it also makes the conditions for the southwestern monsoon less likely to develop. And since the monsoon is the #1 source for precipitation in the desert southwest, a return of El Niño likely means less rain through the first half of the summer. 

Let's add a silver lining to this outlook, shall we? For that, we need to go back to today's drought monitor. Did you notice that nearly the entire state of California is excluded from the drought? 

It's one heck of a difference from where we were at the end of 2022:  

Drought monitor from December 27th, 2022.
Produced by the National Drought Mitigation Center and University of Nebraska, Lincoln

The incredible influx of moisture from multiple atmospheric river events at the beginning of the year caused catastrophic flooding, but the good news is that all the rain and snow essentially ended the drought. And with El Niño conditions expected to return, it's likely that the spigot will stay pointed toward the notoriously drought-stricken state again this winter. 

At long last, is El Nino coming?

Hey there El Niño, it's been a minute! Your sister La Niña had been dominating the Pacific for the past three years. Is it finally time for the warm phase of the El Niño Southern Oscillation, or ENSO, to return? Scientists at the Climate Prediction Center seem to think so. An El Niño Watch has been declared, with the CPC reporting a 62% chance of ENSO-positive conditions developing by the summer.

From January through March, sea surface temperatures in the Niño regions (more on that later) were just slightly below average, signaling a shift into the ENSO Neutral phase. This is the first time since the Fall of 2020 that the La Niña threshold of -0.5°C was not met for three consecutive months. And forecast models are nearly unanimous that the upward temperature trend toward El Niño will continue: 

Forecast model projections for sea surface temperature (SST) anomaly in the Niño 3.4 region.

(Chart from Columbia Climate School IRI for Climate and Society)

Before we dive into the possible impacts of an El Niño summer on the Tri-State, let's define the phenomenon. The onset of El Niño is declared when the surface water in the equatorial Pacific is warmer than average for at least three consecutive months. The map below shows the Niño regions, or specific areas that are closely monitored for ENSO: 

Map of Nino regions from Climate.gov

El Niño is triggered by a weakening of trade winds that normally push warm water away from the coast of equatorial South America. When these winds are weaker, warm water gets trapped along the coastline. The subsequent impacts of this seemingly subtle change can be felt worldwide. 

In the Tri-State area, the impacts of El Niño in the summertime can be subtle. 

Map of El Niño impacts for June through August.
 (Image from Climate.gov)

According to the map above, NOAA does not attribute El Niño to any meaningful change in summertime temperatures or precipitation in the continental USA. However, we can look for clues in previous ENSO-positive summers in the Tri-State. Data from the local National Weather Service office shows that, in this century, summer temperatures were below average in almost every El Niño year. The only exception was during the "Super El Niño" summer of 2015, when temperatures along the equatorial Pacific were nearly 2°C above average, far exceeding the +0.5° threshold. There's not a strong precipitation signal coming from recent El Niño summers, either. Only one stands out, 2009, which was a summer with marginal El Niño conditions. 2009 is still the 4th-wettest summer on record at Central Park. In particular, June was drenched by over ten inches of precipitation, with rain falling on 18 separate days in the month. (Incidentally, this was the same year as "The Summer That Isn't" in New York. Remember that?) 

El Niño conditions tend to have a noticeable impact on Tri-State winters, usually leading to above-average temperatures and rainfall. But, that doesn't mean an El Niño winter is snow-free, as this phase of ENSO tends to bring us more coastal storms like Nor'Easters. In fact, the record-breaking blizzard in January 2016 occurred during the same "Super El Niño" mentioned above! 

One thing that's well documented is the impact of ENSO on hurricane seasons. The tropics tend to be less active during an El Niño, and it has to do with wind shear. In the ENSO-positive phase, the unusually warm water off the west coast of South America repositions the southern jet stream over the Caribbean and subtropical Atlantic, introducing higher wind speeds to the upper atmosphere in this region. Stronger upper-level winds are disruptive to tropical storms, which rely on light wind speeds through the entire vertical column of the atmosphere to strengthen. Learn more about hurricane development here. 

El Niño events typically last for several months to over a year. The La Niña event that ended in March was a bit long for the cool phase of ENSO, but it could be a sign of an overall trend toward a semipermanent La Niña phase. 

When warm becomes the norm: April nearly sets a new bar for heat

 It may already feel like a distant memory with this early-May chill in the air, but April brought some serious heat to the Tri-State. Temperatures reached into the 90s on 2 days of the month, April 13th and 14th. Overall, we finished with an average temperature of 57.6°, making April 2023 the 2nd-warmest on record in NYC. The chart below from New York's local National Weather Service office will need some updating:

Top 10 warmest and coldest Aprils on record.
Data and chart from NWS Upton, NY

With last month added to the list of warmest Aprils, the list will be further stacked with records from this century. By contrast, May has gotten off to a cool start. Both Monday and Tuesday's high temperatures were well below the average high of 68°, and the average temperature for the month is 7° below average so far. However, it's quite unlikely that this month will make it onto the top 10 coldest list below:

Top 10 warmest and coldest Mays on record.
Data and chart from NWS Upton, NY

The rationale is simple, even without knowledge of the upcoming forecast. It's unlikely that this month will be one of the coldest Mays on record because it's been 56 years since May temperatures have been chilly enough to make the list!

 

The near-record warmth in April is just a small part of an ongoing trend, which is easier to see when looking at Central Park's complete records dating all the way back to 1869. 154 years is long enough to have seen lots of ups and downs. But what we've seen instead is an increase in warm temperature records, while cold temperature records have almost disappeared. The chart below shows the number of months on the top 10 record warm versus cold lists through the decades (tied records are included). Again, all data is from NWS New York. 

The trend of record-breaking months may be a better indication of our warming world than the often-cited daily temperature records. While a daily record high can be caused by a brief spike in temperatures or by an unusual weather pattern, the monthly average temperature takes it all into account- highs and lows- through the course of an entire month. 

Despite this early May cooldown, 2023 has been a warm year so far. January set a new record in Central Park; the average temperature of 43.5° was nearly 10 degrees above normal. And February was not far behind. With an average temp of 41.1°, February 2023 will take the #3 spot on the all-time list. A looming El Niño increases the chance for a hot summer in the Tri-State. More on that coming later this week. Stay tuned! 

Summer preview: Last weekend's rain was more than an "April Shower"

We closed out the month of April with a deluge of rain in the Tri-State area. Many spots in and around the city recorded more than 5 inches of rain between Saturday and Sunday's one-two punch of a storm system. Widespread street flooding led to several vehicles stranded on inundated roadways in New York and New Jersey. 

Storms cause flash flooding in the northwest Bronx on April 30th. 
Video courtesy of Melba Kurman/Twitter

Rainfall rates exceeded .5"/hour across the area on Sunday evening, making this late April downpour reminiscent of a July thunderstorm. And as the weekend came to a close, Central Park tallied 5.1" of rain, which is over an inch more than the Park normally records in the entire month of April. 

Rainfall totals from April 28th-30th, 2023.
Graphic created by NWS Upton, NY

A new report by Climate Central shows that these these rainfall events are becoming more common. Across most of the US, even in the desert Southwest, heavy downpours are getting heavier. 

This means that the rainfall rate is increasing, even in places where the average annual precipitation has decreased in recent decades. Why does rainfall rate matter? When rain falls in short intense bursts rather than slowly and steadily, flash flooding is more likely. Flash floods can make roadways impassable, as we experienced firsthand over the weekend. Even more importantly, people can get trapped in floodwaters, as they're more likely to be unprepared for the sudden rise in water levels. It's also bad news for agriculture and maintaining a reliable water supply, with less rainwater having a chance to penetrate into aquifers.  

The Northeast region as a whole has seen a 13% increase in hourly rainfall intensity. NYC's report, indicated by a brownish dot in the graphic above, is the only location in the region with a slight downward trend since 1970.

The trend line indicates that rainfall intensity has dropped by about 0.005"/hour since 1970. The argument could be made that this isn't a statistically significant change, as any rainfall amount under 0.01" is recorded as a trace (T) by the National Weather Service. With all other surveyed sites in the Northeast seeing an increase in heavy downpours, NYC's slight decrease is an anomaly. And with summer being the wettest season in the Tri-State, more heavy storms are likely lurking in the months to come.