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Category 6 has moved! See the latest from Dr. Jeff Masters and Bob Henson here.NOAA Gins Up Major El Niño Field Campaign: Hurricane Pali Spins Southwest of Hawaii
Scientists at NOAA will be putting the well-predicted “super” El Niño of 2015-16 under a mammoth microscope over the next three months. With just enough time to line up some big observing platforms--plus a lot of other things going right--NOAA/ESRL’s Physical Sciences Division (PSD) has managed to pull together a major field effort that will analyze the mechanics of this El Niño in truly unprecedented detail.
“We’re trying to plan a field campaign in three months that would normally take two to three years,” Ryan Spackman told me in a phone chat. Spackman, an ESRL-based program manager with Science and Technology Corporation, is working with ESRL senior scientist Randy Dole to oversee the NOAA El Niño Rapid Response Field Campaign. “There are still some loose ends, but there are no show-stoppers at this point,” Spackman said. “Things are converging very quickly--which, frankly, they need to be.”
Figure 1. Sea-surface height as inferred by by NASA satellites during the current El Niño (December 27, 2015, at left, from Jason-2) and at a comparable point during the last “super” El Niño (December 28, 1997, at right, from TOPEX/Poseidon). Warmer temperatures in the upper ocean result in higher sea-surface heights, as the seawater expands. In 1997, the above-average sea surface height was generally more intense and peaked in November. In 2015, the area of high sea levels was less pronounced but considerably broader. Image credit: NASA/JPL-Caltech.
Sonde science: Gathering data on El Niño where it matters most
The crucial science question driving this field campaign is exactly how the upward-flowing energy across the El Niño region of the eastern tropical Pacific affects the surrounding atmosphere. It’s well known that the warm sea-surface temperatures (SSTs) associated with El Niño help displace showers and thunderstorms (convection) much further east than they normally roam, closer to Peru than their usual home near Indonesia. The rising motion in those storms sets off a chain of events that propagate outward for thousands of miles. Toward the top of the troposphere, or at roughly 10-15 km (6-9 miles) above the El Niño region, the updrafts of convective towers force high-altitude air to flow outward, just as it would from a hurricane.
“It’s that diverging air that has an impact on the subtropical jet, extending it and enhancing it,” said Spackman. In turn, the strengthened subtropical jet has impacts on weather downstream at mid-latitudes, including enhanced winter rainfall from California all the way to Florida. “We can draw these links, but we don’t have many observations from the El Niño region, and our weather prediction models don’t include all the underlying physics they need to model that process,” Spackman said. Not surprisingly, a number of studies have pointed to the El Niño region as being a key source of larger-scale model uncertainty during El Niño episodes.
To get a handle on what’s going on this winter, a vast number of atmospheric profiles--potentially more than 1000, which is a hefty number indeed for such a project--will be collected in two ways:
--radiosondes (balloon-borne instrument packages launched from ship or shore)
--dropsondes (parachute-borne instrument packages deposited from aircraft)
Radiosondes have been a mainstay of routine weather observing since the 1930s. Despite the immense value of satellites, there is still no substitute for the data that a radiosonde or dropsonde can gather. Wind data, in particular, are often difficult for satellites to obtain with precision, especially in the presence of multiple cloud layers. The sonde-derived profiles this winter will be collected over a domain spanning thousands of miles, but the focal point, as one might expect, is the area of unusual oceanic warmth now being produced by El Niño over the central and eastern tropical Pacific.
Figure 2. Left: NOAA’s Gulfstream-IV jet has flown on hurricane and winter-storm reconnaissance missions since 1996. Image credit: NOAA. Right: A view of NASA's Global Hawk unmanned aircraft from one of its wings. Image credit: NASA.
Two aircraft, a ship, and an island
The first platform for the project is NOAA’s Gulfstream-IV hurricane-hunter aircraft (see Figure 2 above). The high-flying Gulfstream-IV is typically used to monitor the atmosphere around hurricanes, so it’s an ideal tool for sampling how the El Niño convection is affecting the surrounding air at high altitudes. Up to 20 G-IV missions will be conducted between January 19 and March 3 from a home base at Honolulu International Airport, with as many as 30 dropsondes to be deployed per mission. “We’ll be transiting quite a bit to get to the intertropical convergence zone near the equator,” says Spackman. “Probably half of each flight will be just getting there.”
The Niño3.4 region is the “meat of where we’re going to operate--nominally from the dateline to about 130°W. It’s going to be a stretch to get very far to the west and the east, so we expect a couple of deployments out of Tahiti or perhaps American Samoa.” This will allow for a broader study area, including the Niño4 region further west, where this year’s El Niño has been particularly strong. Along with the dropsondes, the G-IV’s tail-mounted Doppler radar will be invaluable for gathering wind data, said Spackman.
Figure 3. Areas of the equatorial Pacific that are monitored to produce weekly, monthly, and seasonal estimates of the evolution of El Niño and its counterpart, La Niña. Variations in the Niño3.4 sea surface temperature (center) are the most common index of El Niño strength. Image credit: NOAA/NCEI.
The relatively quiet Atlantic hurricane season of 2015 turned out to be a boon for El Niño research, as it left open many potential flight hours for a second platform (see Figure 2 above): NASA’s Global Hawk unmanned aerial system (UAS), based at NASA Armstrong Flight Research Center (Edwards Air Force Base, California). The El Niño sampling will piggyback onto the Global Hawk’s previously planned missions for an activity called SHOUT: Sensing Hazards with Operational Unmanned Technology. The idea behind SHOUT is to gather focused data from mid-latitude and subtropical regions identified as crucial to an unfolding weather scenario (e.g., a developing storm far out in the Pacific) in order to improve forecasts over the United States several days later. “We’re hoping we can devise flight strategies where we coordinate the G-IV flights at lower latitudes with what SHOUT is doing at higher latitudes,” Spackman said.
The El Niño project will be able to draw on as many as six 24-hour flights during three weeks in February. Each flight will carry and deploy up to 75 dropsondes, with the flights operated remotely from NASA/Armstrong and the sondes launched with a system developed at the National Center for Atmospheric Research.
Figure 4. NOAA Ship Ronald H. Brown, a research vessel named in honor of the late U.S. Secretary of Commerce, has been carrying out missions around the world since 1997. Here, two workers from the Ron Brown examine a buoy in the Tropical Atmosphere Ocean (TAO) array (left). Image credit: NOAA, courtesy Oak Ridge National Laboratory.
Another platform--NOAA’s Ronald H. Brown research vessel (Figure 4, above) is part of the project thanks to another happy coincidence. The Ron Brown was already scheduled to be plying the eastern tropical Pacific from mid-February to mid-March to carry out maintenance on the dozens of buoys that monitor the atmosphere and ocean across the region (among other things, helping to detect El Niño itself). For the new field project, two PSD staff will launch 6 to 8 radiosondes each day, around the clock, from aboard the ship as it hops from buoy to buoy along a zigzagging path from Hawaii to California.
There’s also Kiritimati (also known as Christmas Island), one of the Line Islands. Routine radiosonde launches from this remote site were discontinued years ago, but it’s in a prime location for this project: at 2°N, due south of Hawaii and near the heart of the sea-surface warming of El Niño. Two radiosondes a day will be launched from the island from January 23 to March 28.
Figure 5. A view of Kiritimati from the International Space Station. The world’s largest coral atoll by land area, Kiritimati covers about 150 square miles, with a population of around 5,000. Image credit: NASA/Wikimedia Commons.
Along with the four platforms above, a 3-centimeter-wavelength radar will be deployed in the south San Francisco Bay area. It will help fill a gap in the existing national network of Doppler radars, thus leading to more accurate rainfall estimates for the central California coast.
As it compiles an irreplaceable trove of data for research, ESRL will also feed many of those observations into the network of real-time data used by numerical forecast models around the world. The enhanced data will thus help improve the day-to-day forecasts produced this winter by NOAA, ECMWF, and other leading centers (although the Global Hawk data are not yet certified for operational use by NOAA). "In many ways, this is a ripe playground for the SHOUT program," Spackman said. ”Their goal is to demonstrate that targeted observations have an impact on select high-impact forecast metrics such as precipitation."
Figure 6. A cross section of the dominant circulation cells affecting the Northern Hemisphere, going from north to south as you move from left to right. The showers and thunderstorms (convection) depicted at right shift from the western Pacific closer to the Americas during El Niño, which alters the downstream effects on the subtropical jet stream. Image credit: CMMAP/Colorado State University.
More on the project from Randy Dole
I asked ESRL’s Randy Dole to weigh in on how ESRL was able to pull together such an ambitious field project on short notice, and what the effort might tell us about how El Niño works.
BH: How exactly do the warm equatorial SSTs associated with El Niño act to strengthen the subtropical jet? Is it simply due to a strengthening of the Hadley circulation, or are there additional processes going on as well?
RD: “There are multiple factors, but you've got the primary one. Tropical convection usually focuses near the warmest waters, which are shifted eastward in El Niño years. Poleward flow diverging from near the top of the convection turns eastward when viewed in the earth's frame of reference (i.e.,through the Coriolis force). Eastward turning occurs in both hemispheres, so unusually strong subtropical westerly jet streams occur in both Northern and Southern hemispheres related to El Niño. Because El Niño-related convective enhancement occurs mainly in the central to eastern tropical Pacific, the jet strengthening is typically seen over the central and eastern subtropical Pacific.”
BH: How does this year’s campaign compare to what happened during the last “super” El Niño?
RD: ”In 1997-98 there was no rapid rapid response field campaign over the tropical Pacific, although one might have been possible. To be sure, there were flights for the NORPEX field campaign, but these were primarily conducted to perform targeted observations in the extratropical northeast North Pacific aiming at improving short-term forecasts. Spinning up a rapid response field campaign, as opposed to tweaking a campaign that was already planned, requires many factors, including the ability to anticipate such an event and its potential impacts. Typically, planning and developing logistical support for a campaign of the scale we plan to conduct takes 2-3 years, rather than a few months. So it's a daunting challenge, and hard to know whether those around in 1998 even conceived such a thing. Since 1998 the NASA Global Hawk has become available, so that adds to a capability that would not have existed in 1998. But in the end, in addition to an event driver, it takes many factors to come together: the will, hard work, and support from leadership to shift out of business-as-usual, the default option. The closest analogy we could come up with in NOAA was the agency's Deepwater Horizon response, but that was in reaction to a disaster, rather than being proactive, as we are trying to be here.”
Figure 7. The domain for the NOAA El Niño Rapid Response Field Campaign atop a map of recent sea-surface temperatures (redder colors indicate warmer temperatures relative to the seasonal average). Image credit: NOAA/ESRL.
BH: What's an example of a burning-curiosity question for you that you hope can be answered through these various observations?
RD: ”First, I would like to resolve how well our current weather and climate models do in representing the tropical atmospheric response to a major El Niño. In the absence of direct observations, it's difficult to be sure. My strong suspicion is that the models have major errors and, if so, those errors will be apparent in our observations. As this is the first link in the chain from El Niño to West Coast rainfall, knowing how well our models simulate this link is critical.
“Second, if there are significant tropical errors, how important are they for NOAA forecasts, and over what time scale? The observations may not answer that question directly, but they will point us in the direction of what we will need to do to find out, and what the implications will be for NOAA's future observing and forecast modeling systems. The challenges are common to weather and climate models, as tropical errors will influence everything from short-term predictions to longer-term climate change projections.
“Third, at heart I simply want to understand how the system works. Roughly, from an atmospheric perspective we might consider that El Niño as turning up a "knob" on ocean conditions, and when the knob is turned to very high heavy winter rainfall is much more likely in California. But what are the most important factors determining this relationship? It's easy to conjecture, but I would like to see these observations bring us closer to providing definitive answers. In the long run that will help us identify what will be needed to improve predictions of variables that matter to the public and decision-makers.”
Organizers of the NOAA El Niño Rapid Response Field Campaign will provide an overview of the field campaign and related partnerships at this week’s 96th Annual Meeting of the American Meteorological Society in New Orleans (7:00 - 8:30 pm Tuesday, room 243 of the Ernest N. Morial Convention Center). You can follow news about the project at the dedicated ESRL website.
Figure 8. Infrared satellite image of Hurricane Pali as of 1330Z (8:30 am EST) Tuesday, January 12, 2015. Image credit: NOAA/NESDIS.
Figure 9. MODIS visible satellite image of Hurricane Pali taken at 5:30 pm EST January 11, 2016. At the time, Pali was intensifying into a Category 1 storm with 85 mph winds. Image credit: NASA.
Strange times in the tropics: Hurricane Pali in the Central Pacific; possible subtropical storm in the North Atlantic
It’s not entirely out of the question that a tropical cyclone will be churning over or just west of the Central Pacific the field campaign kicks off next week. Late Monday night, Hurricane Pali became the earliest hurricane on record for both the Central and Northeast Pacific (the region between the International Date Line and the Americas), beating 1992’s Ekeka, which became a hurricane on January 30. Still packing winds of 85 mph early Tuesday morning, Pali was located unusually close to the equator--at 7.5°N, 171.6°W, or about 1300 miles southwest of Honolulu--and was moving south-southeast at about 7 mph. Pali should continue drifting equatorward over the next several days, gradually bending toward the west and potentially back toward the west-northwest if it hangs on. Sea-surface temperatures are more than warm enough to support Pali along its projected track, at 28-29°C (82-84°F). However, moderate wind shear (10 - 20 knots) could keep Pali from strengthening, and there are few historical precedents for tropical cyclones at such low latitudes. In its 4:00 am EST update, the Central Pacific Hurricane Center noted: “It is fair to say the uncertainty is higher than normal as Pali moves closer to the equator.” Wunderblogger Lee Grenci has a Tuesday morning post analyzing the possibility that Pali could cross the equator--something no tropical cyclone has ever been observed to do.
Meanwhile, a tenacious extratropical storm over the Central North Atlantic still has a chance to take on subtropical characteristics later this week as it angles southeast, east of 40°W longitude. The National Hurricane Center gives this system a 40% chance of development through Sunday. Sea-surface temperatures are on the cool side for a fully tropical system, though.
Bob Henson
“We’re trying to plan a field campaign in three months that would normally take two to three years,” Ryan Spackman told me in a phone chat. Spackman, an ESRL-based program manager with Science and Technology Corporation, is working with ESRL senior scientist Randy Dole to oversee the NOAA El Niño Rapid Response Field Campaign. “There are still some loose ends, but there are no show-stoppers at this point,” Spackman said. “Things are converging very quickly--which, frankly, they need to be.”
Figure 1. Sea-surface height as inferred by by NASA satellites during the current El Niño (December 27, 2015, at left, from Jason-2) and at a comparable point during the last “super” El Niño (December 28, 1997, at right, from TOPEX/Poseidon). Warmer temperatures in the upper ocean result in higher sea-surface heights, as the seawater expands. In 1997, the above-average sea surface height was generally more intense and peaked in November. In 2015, the area of high sea levels was less pronounced but considerably broader. Image credit: NASA/JPL-Caltech.
Sonde science: Gathering data on El Niño where it matters most
The crucial science question driving this field campaign is exactly how the upward-flowing energy across the El Niño region of the eastern tropical Pacific affects the surrounding atmosphere. It’s well known that the warm sea-surface temperatures (SSTs) associated with El Niño help displace showers and thunderstorms (convection) much further east than they normally roam, closer to Peru than their usual home near Indonesia. The rising motion in those storms sets off a chain of events that propagate outward for thousands of miles. Toward the top of the troposphere, or at roughly 10-15 km (6-9 miles) above the El Niño region, the updrafts of convective towers force high-altitude air to flow outward, just as it would from a hurricane.
“It’s that diverging air that has an impact on the subtropical jet, extending it and enhancing it,” said Spackman. In turn, the strengthened subtropical jet has impacts on weather downstream at mid-latitudes, including enhanced winter rainfall from California all the way to Florida. “We can draw these links, but we don’t have many observations from the El Niño region, and our weather prediction models don’t include all the underlying physics they need to model that process,” Spackman said. Not surprisingly, a number of studies have pointed to the El Niño region as being a key source of larger-scale model uncertainty during El Niño episodes.
To get a handle on what’s going on this winter, a vast number of atmospheric profiles--potentially more than 1000, which is a hefty number indeed for such a project--will be collected in two ways:
--radiosondes (balloon-borne instrument packages launched from ship or shore)
--dropsondes (parachute-borne instrument packages deposited from aircraft)
Radiosondes have been a mainstay of routine weather observing since the 1930s. Despite the immense value of satellites, there is still no substitute for the data that a radiosonde or dropsonde can gather. Wind data, in particular, are often difficult for satellites to obtain with precision, especially in the presence of multiple cloud layers. The sonde-derived profiles this winter will be collected over a domain spanning thousands of miles, but the focal point, as one might expect, is the area of unusual oceanic warmth now being produced by El Niño over the central and eastern tropical Pacific.
Figure 2. Left: NOAA’s Gulfstream-IV jet has flown on hurricane and winter-storm reconnaissance missions since 1996. Image credit: NOAA. Right: A view of NASA's Global Hawk unmanned aircraft from one of its wings. Image credit: NASA.
Two aircraft, a ship, and an island
The first platform for the project is NOAA’s Gulfstream-IV hurricane-hunter aircraft (see Figure 2 above). The high-flying Gulfstream-IV is typically used to monitor the atmosphere around hurricanes, so it’s an ideal tool for sampling how the El Niño convection is affecting the surrounding air at high altitudes. Up to 20 G-IV missions will be conducted between January 19 and March 3 from a home base at Honolulu International Airport, with as many as 30 dropsondes to be deployed per mission. “We’ll be transiting quite a bit to get to the intertropical convergence zone near the equator,” says Spackman. “Probably half of each flight will be just getting there.”
The Niño3.4 region is the “meat of where we’re going to operate--nominally from the dateline to about 130°W. It’s going to be a stretch to get very far to the west and the east, so we expect a couple of deployments out of Tahiti or perhaps American Samoa.” This will allow for a broader study area, including the Niño4 region further west, where this year’s El Niño has been particularly strong. Along with the dropsondes, the G-IV’s tail-mounted Doppler radar will be invaluable for gathering wind data, said Spackman.
Figure 3. Areas of the equatorial Pacific that are monitored to produce weekly, monthly, and seasonal estimates of the evolution of El Niño and its counterpart, La Niña. Variations in the Niño3.4 sea surface temperature (center) are the most common index of El Niño strength. Image credit: NOAA/NCEI.
The relatively quiet Atlantic hurricane season of 2015 turned out to be a boon for El Niño research, as it left open many potential flight hours for a second platform (see Figure 2 above): NASA’s Global Hawk unmanned aerial system (UAS), based at NASA Armstrong Flight Research Center (Edwards Air Force Base, California). The El Niño sampling will piggyback onto the Global Hawk’s previously planned missions for an activity called SHOUT: Sensing Hazards with Operational Unmanned Technology. The idea behind SHOUT is to gather focused data from mid-latitude and subtropical regions identified as crucial to an unfolding weather scenario (e.g., a developing storm far out in the Pacific) in order to improve forecasts over the United States several days later. “We’re hoping we can devise flight strategies where we coordinate the G-IV flights at lower latitudes with what SHOUT is doing at higher latitudes,” Spackman said.
The El Niño project will be able to draw on as many as six 24-hour flights during three weeks in February. Each flight will carry and deploy up to 75 dropsondes, with the flights operated remotely from NASA/Armstrong and the sondes launched with a system developed at the National Center for Atmospheric Research.
Figure 4. NOAA Ship Ronald H. Brown, a research vessel named in honor of the late U.S. Secretary of Commerce, has been carrying out missions around the world since 1997. Here, two workers from the Ron Brown examine a buoy in the Tropical Atmosphere Ocean (TAO) array (left). Image credit: NOAA, courtesy Oak Ridge National Laboratory.
Another platform--NOAA’s Ronald H. Brown research vessel (Figure 4, above) is part of the project thanks to another happy coincidence. The Ron Brown was already scheduled to be plying the eastern tropical Pacific from mid-February to mid-March to carry out maintenance on the dozens of buoys that monitor the atmosphere and ocean across the region (among other things, helping to detect El Niño itself). For the new field project, two PSD staff will launch 6 to 8 radiosondes each day, around the clock, from aboard the ship as it hops from buoy to buoy along a zigzagging path from Hawaii to California.
There’s also Kiritimati (also known as Christmas Island), one of the Line Islands. Routine radiosonde launches from this remote site were discontinued years ago, but it’s in a prime location for this project: at 2°N, due south of Hawaii and near the heart of the sea-surface warming of El Niño. Two radiosondes a day will be launched from the island from January 23 to March 28.
Figure 5. A view of Kiritimati from the International Space Station. The world’s largest coral atoll by land area, Kiritimati covers about 150 square miles, with a population of around 5,000. Image credit: NASA/Wikimedia Commons.
Along with the four platforms above, a 3-centimeter-wavelength radar will be deployed in the south San Francisco Bay area. It will help fill a gap in the existing national network of Doppler radars, thus leading to more accurate rainfall estimates for the central California coast.
As it compiles an irreplaceable trove of data for research, ESRL will also feed many of those observations into the network of real-time data used by numerical forecast models around the world. The enhanced data will thus help improve the day-to-day forecasts produced this winter by NOAA, ECMWF, and other leading centers (although the Global Hawk data are not yet certified for operational use by NOAA). "In many ways, this is a ripe playground for the SHOUT program," Spackman said. ”Their goal is to demonstrate that targeted observations have an impact on select high-impact forecast metrics such as precipitation."
Figure 6. A cross section of the dominant circulation cells affecting the Northern Hemisphere, going from north to south as you move from left to right. The showers and thunderstorms (convection) depicted at right shift from the western Pacific closer to the Americas during El Niño, which alters the downstream effects on the subtropical jet stream. Image credit: CMMAP/Colorado State University.
More on the project from Randy Dole
I asked ESRL’s Randy Dole to weigh in on how ESRL was able to pull together such an ambitious field project on short notice, and what the effort might tell us about how El Niño works.
BH: How exactly do the warm equatorial SSTs associated with El Niño act to strengthen the subtropical jet? Is it simply due to a strengthening of the Hadley circulation, or are there additional processes going on as well?
RD: “There are multiple factors, but you've got the primary one. Tropical convection usually focuses near the warmest waters, which are shifted eastward in El Niño years. Poleward flow diverging from near the top of the convection turns eastward when viewed in the earth's frame of reference (i.e.,through the Coriolis force). Eastward turning occurs in both hemispheres, so unusually strong subtropical westerly jet streams occur in both Northern and Southern hemispheres related to El Niño. Because El Niño-related convective enhancement occurs mainly in the central to eastern tropical Pacific, the jet strengthening is typically seen over the central and eastern subtropical Pacific.”
BH: How does this year’s campaign compare to what happened during the last “super” El Niño?
RD: ”In 1997-98 there was no rapid rapid response field campaign over the tropical Pacific, although one might have been possible. To be sure, there were flights for the NORPEX field campaign, but these were primarily conducted to perform targeted observations in the extratropical northeast North Pacific aiming at improving short-term forecasts. Spinning up a rapid response field campaign, as opposed to tweaking a campaign that was already planned, requires many factors, including the ability to anticipate such an event and its potential impacts. Typically, planning and developing logistical support for a campaign of the scale we plan to conduct takes 2-3 years, rather than a few months. So it's a daunting challenge, and hard to know whether those around in 1998 even conceived such a thing. Since 1998 the NASA Global Hawk has become available, so that adds to a capability that would not have existed in 1998. But in the end, in addition to an event driver, it takes many factors to come together: the will, hard work, and support from leadership to shift out of business-as-usual, the default option. The closest analogy we could come up with in NOAA was the agency's Deepwater Horizon response, but that was in reaction to a disaster, rather than being proactive, as we are trying to be here.”
Figure 7. The domain for the NOAA El Niño Rapid Response Field Campaign atop a map of recent sea-surface temperatures (redder colors indicate warmer temperatures relative to the seasonal average). Image credit: NOAA/ESRL.
BH: What's an example of a burning-curiosity question for you that you hope can be answered through these various observations?
RD: ”First, I would like to resolve how well our current weather and climate models do in representing the tropical atmospheric response to a major El Niño. In the absence of direct observations, it's difficult to be sure. My strong suspicion is that the models have major errors and, if so, those errors will be apparent in our observations. As this is the first link in the chain from El Niño to West Coast rainfall, knowing how well our models simulate this link is critical.
“Second, if there are significant tropical errors, how important are they for NOAA forecasts, and over what time scale? The observations may not answer that question directly, but they will point us in the direction of what we will need to do to find out, and what the implications will be for NOAA's future observing and forecast modeling systems. The challenges are common to weather and climate models, as tropical errors will influence everything from short-term predictions to longer-term climate change projections.
“Third, at heart I simply want to understand how the system works. Roughly, from an atmospheric perspective we might consider that El Niño as turning up a "knob" on ocean conditions, and when the knob is turned to very high heavy winter rainfall is much more likely in California. But what are the most important factors determining this relationship? It's easy to conjecture, but I would like to see these observations bring us closer to providing definitive answers. In the long run that will help us identify what will be needed to improve predictions of variables that matter to the public and decision-makers.”
Organizers of the NOAA El Niño Rapid Response Field Campaign will provide an overview of the field campaign and related partnerships at this week’s 96th Annual Meeting of the American Meteorological Society in New Orleans (7:00 - 8:30 pm Tuesday, room 243 of the Ernest N. Morial Convention Center). You can follow news about the project at the dedicated ESRL website.
Figure 8. Infrared satellite image of Hurricane Pali as of 1330Z (8:30 am EST) Tuesday, January 12, 2015. Image credit: NOAA/NESDIS.
Figure 9. MODIS visible satellite image of Hurricane Pali taken at 5:30 pm EST January 11, 2016. At the time, Pali was intensifying into a Category 1 storm with 85 mph winds. Image credit: NASA.
Strange times in the tropics: Hurricane Pali in the Central Pacific; possible subtropical storm in the North Atlantic
It’s not entirely out of the question that a tropical cyclone will be churning over or just west of the Central Pacific the field campaign kicks off next week. Late Monday night, Hurricane Pali became the earliest hurricane on record for both the Central and Northeast Pacific (the region between the International Date Line and the Americas), beating 1992’s Ekeka, which became a hurricane on January 30. Still packing winds of 85 mph early Tuesday morning, Pali was located unusually close to the equator--at 7.5°N, 171.6°W, or about 1300 miles southwest of Honolulu--and was moving south-southeast at about 7 mph. Pali should continue drifting equatorward over the next several days, gradually bending toward the west and potentially back toward the west-northwest if it hangs on. Sea-surface temperatures are more than warm enough to support Pali along its projected track, at 28-29°C (82-84°F). However, moderate wind shear (10 - 20 knots) could keep Pali from strengthening, and there are few historical precedents for tropical cyclones at such low latitudes. In its 4:00 am EST update, the Central Pacific Hurricane Center noted: “It is fair to say the uncertainty is higher than normal as Pali moves closer to the equator.” Wunderblogger Lee Grenci has a Tuesday morning post analyzing the possibility that Pali could cross the equator--something no tropical cyclone has ever been observed to do.
Meanwhile, a tenacious extratropical storm over the Central North Atlantic still has a chance to take on subtropical characteristics later this week as it angles southeast, east of 40°W longitude. The National Hurricane Center gives this system a 40% chance of development through Sunday. Sea-surface temperatures are on the cool side for a fully tropical system, though.
Bob Henson
#Pali and Ekeka (1992) are the only two hurricanes to form in the Northeast Pacific (E of 180W) prior to May. pic.twitter.com/4p9utxsOiH
— Philip Klotzbach (@philklotzbach) January 12, 2016The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.