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Infrared GOES-16 image of Tropical Storm Nate (located offshore just east of Nicaragua) and the huge swath of showers and thunderstorms in both the Caribbean and Pacific feeding into the newly designated storm. NASA / MSFC Earth Science Branch. GOES-16 imagery is considered preliminary and non-operational.
By Dr. Jeff Masters and Bob Henson
Tropical Storm Nate formed at 8 a.m. EDT Thursday morning in the Southwestern Caribbean near the coast of Nicaragua, and is bringing torrential rains to portions of Nicaragua and Costa Rica as it moves northwest at 9 mph. Nate will be a significant rainfall threat to Central America over the next two days, and is likely to threaten Mexico's Yucatan Peninsula as a tropical storm or Category 1 hurricane on Friday, and arrive on the U.S. Gulf Coast this weekend as a hurricane.
Figure 1. GOES-16 view of Tropical Storm Nate, at 10:15 a.m. EDT Oct. 5.
Nate made landfall over northeastern Nicaragua late Thursday morning as a tropical storm with 40 mph winds, and tropical storm warnings are up for much of the coast of Nicaragua and Honduras. However, the main danger to Central America from Nate will be torrential rains: 15 – 20" in Nicaragua, 5 – 10" in Panama and Costa Rica, and 4 - 8" in Honduras and the eastern Yucatan Peninsula. Much of the heavy rain in Nicaragua, Coast Rica and Panama will occur on the Pacific side, as Nate's large circulation pulls moisture from the Pacific across Central America and into the Southwest Caribbean. Satellite rainfall estimates show that the heaviest rains from Nate thus far have been on the Pacific side of Costa Rica and Panama, where more than 8" of rain has fallen over the past 7 days. A personal weather station on the Pacific coast of Nicaragua recorded 3.34"of rain in the 12 hours beginning at 6 p.m. Wednesday.
Figure 2. The 11 a.m. Thursday NHC forecast for the probability of tropical-storm-force winds for the five days ending on Oct. 10. New Orleans was given about a 50 percent chance of tropical storm-force winds of 39+ mph, with those winds most likely to arrive on Saturday night. Cancun and Cozumel were also given about a 50 percent chance of seeing tropical storm-force winds, with the onset occurring late Friday afternoon.
Satellite imagery early Thursday afternoon showed that although the intensity of Nate's heavy thunderstorms had waned slightly after the center made landfall, the overall structure of the storm was holding together, with the low-level spiral bands remaining prominent. Conditions were favorable for development, with moderate wind shear of 10 - 20 knots, sea surface temperatures (SSTs) a very warm 30°C (86°F) and an unusually moist atmosphere with a mid-level relative humidity of 85 percent.
Figure 3. Ocean Heat Content (OHC) for Oct. 5. Forecast positions for Nate from the 11 a.m. EDT Thursday NHC forecast are also shown. OHC values in excess of 80 kilojoules per square centimeter (yellow-green colors) are often associated with rapid intensification of hurricanes. Nate is expected to be passing near or over two areas of very high ocean heat content, with very warm waters that extend to great depth: in the Western Caribbean off the coast of Yucatan Peninsula, and again in the Gulf of Mexico, over the northern portion of the Loop Current, where a warm eddy appears to be attempting to break off.
Short-Term Forecast for Nate
Once Nate finishes its traverse of northeastern Honduras on Thursday evening and emerges into the Western Caribbean, the storm will be in a very favorable environment for intensification. The 12Z Thursday run of the SHIPS model predicted that wind shear would be low to moderate, 5 – 15 knots, through Saturday. SSTs will be a very warm 30°C (86°F), and Nate will have an unusually moist atmosphere, with a mid-level relative humidity of 80 – 85 percent. Nate will be passing over an area of very high ocean heat content (OHC) in the Western Caribbean, with very warm waters that extend to great depth. Since Nate is unlikely to emerge from Honduras as a well-organized system, it will probably take the storm about 12 hours to get organized and take full advantage of these favorable conditions.
The Thursday morning runs of our top five intensity models showed modest intensification of Nate on Thursday evening through Friday evening, with none of the models predicting that Nate would be a hurricane when it makes its closest approach to Cozumel and the northeastern tip of Mexico's Yucatan Peninsula on Friday night. However, the 12Z Thursday SHIPS model Rapid Intensification Index gave Nate a 40 percent chance of being a Category 1 hurricane with 75 mph winds by 8 a.m. Friday, 12 hours before it will make its closest pass to the Cozumel/Cancun area. The way this hurricane season has gone, it is safer to predict intensification at the upper end of what our intensity models are predicting, and residents and visitors in Cozumel/Cancun should expect that Nate will be a Category 1 hurricane Friday evening when it makes its closest pass.
A hurricane watch and tropical storm warnings are now in effect for the resort cities of Cancun and Cozumel and other parts of the northeast Yucatan. Nate's rains will not be as heavy here as in Central America, but local totals of 12" or more are possible. High tide at Cozumel and Cancun is at 9:37 p.m. CDT Friday, and it will be one of the highest high tides to the year, due to the full moon. Tidal range at Cozumel/Cancun between low and high tide is only about 0.6 - 0.8 feet (.18 - .25 meters), so the timing of Nate's storm surge with respect to the high tide is less important than we see for most locations along the U.S. coast.
Nate's Landfall on the U.S. Gulf Coast
Interaction with the flat terrain of the Yucatan may have little impact on Nate's strength, but it is also possible that passage over the Yucatan will disrupt the storm's core and halt strengthening for a half-day or so. As Nate begins moving away from the Yucatan Peninsula early Saturday, it will be moving into a zone of much stronger upper-level steering, which will pull the storm to the north or north-northwest at an accelerating rate. Nate is expected to cross the Gulf of Mexico in 24 to 30 hours, an unusually rapid clip. Nate's potential strengthening will be blunted by the wind shear associated with the strong steering flow, as well as by the rapid motion itself, which will limit its time over water. As Nate approaches the Gulf Coast, it will encounter cooler SSTs and a lower oceanic heat content, which may slow or halt intensification.
Figure 4. Left: Weather Underground depiction of NHC's 3-day forecast for Tropical Storm Nate from 11 a.m. EDT Oct. 5. Right: Hurricane Opal strengthened from Category 1 to 4 in October 1995 as it raced toward the central Gulf Coast after spending about 24 hours just offshore from the Yucatan Peninsula. Nate is not expected to linger near the Yucatan.
In October 1995, Hurricane Opal rocketed from Category 1 to high-end Category 4 strength while moving from just west of the Yucatan to the Florida Panhandle in about 24 hours (see Figure 4 above). However, Opal lingered and organized for roughly a day just off the Yucatan before starting its northward charge. Nate is unlikely to be as well structured as Opal when it starts its quick northward trek. Our best intensity guidance, including the HWRF and HMON models, suggest that Nate will reach the central U.S. Gulf Coast as a Category 1 or perhaps Category 2 hurricane. These are the most likely outcomes, although it is too soon to rule out the possibility that Nate could become a major hurricane if it moves slowly enough over the southern and central Gulf, where SSTs are above 29°C (84°F). The increasing upper-level southerly winds may also provide an outflow channel for Nate, which would facilitate intensification. The SHIPS model Rapid Intensification Index from 12Z Thursday morning showed a 48 percent chance of Nate gaining 65 knots of strength by Sunday, which would bring it to the Category 3 threshold (115 mph winds.) Whatever its strength, Nate will be approaching the Gulf Coast unusually quickly, so residents should take this rapid speed into account.
Figure 6. The 0Z Oct. 5 track forecast by the members of the GFS model ensemble. Only about two-thirds of the GFS ensembles brought Nate into the Gulf of Mexico as a tropical storm, and none brought Nate to hurricane strength.
Models agree that Nate will make landfall between late Saturday night and midday Sunday, most likely somewhere between southeast Louisiana and the western Florida Panhandle. There was a significant shift west in the model consensus on Wednesday night: The European and other models fell into line with the GFS, which had been calling for a more leftward track into far southeast Louisiana. This is a good time to keep in mind that even a superior model overall (such as the Euro) may not be the best model on any given storm or on any given day. The Euro and GFS aren't so much like a pro baseball pitcher and a high-school pitcher; they are more like two excellent pro pitchers, one of whom has slightly better stats, but either of whom might pitch the better game next Saturday night.
Storm Surge
Storm surge is a particular concern with Nate. Much of the stretch of the central Gulf Coast from southeast Louisiana to the western Florida Panhandle is quite vulnerable to storm surge. Exact surge values will depend on Nate's strength and specific track, but it's not too soon for coastal dwellers to be aware of the risk and to begin preparing for it. Although the range between low and high tide is not extremely large along the central Gulf Coast, some of the highest astronomical tides of the year will be occurring this weekend into early next week. From Biloxi to Pensacola, high tide occurs around midnight, with the main low tide in the morning. If Nate moves as fast as some models are projecting, it could arrive during the high part of this cycle early Sunday. Because Nate will be moving so quickly, its surge impact is unlikely to extend beyond one tidal cycle.
Rain
By the time Nate reaches the U.S., its quick movement will help limit the risk of extreme rainfall totals. A swath of 3 – 6" can be expected within about 150 miles of Nate's center, from the Gulf Coast north across the Appalachians to parts of New York and/or New England.
Figure 7. 7-day precipitation outlook for the period from 8 a.m. EDT Oct. 5 to Oct. 12. The exact placement of the band of heavy rain associated with Nate over the eastern U.S. will hinge on Nate's eventual motion.
Reposted with permission from our media associate Weather Underground.
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By Bob Henson
The strong, recurrent Pacific jet stream that's been delivering massive amounts of rain to California has also been pushing mild Pacific air downslope off the Rockies and eastward, keeping the southern two-thirds of the U.S. absurdly warm for early February. From New Mexico to Virginia southward to the Gulf Coast, trees and shrubs are budding out en masse up to three weeks ahead of schedule (see Figure 1).
"It's Official: 2016 Was the Hottest Year Ever Recorded" via @ClimateNexus/@EcoWatch: https://t.co/meonGdUrDY— Michael E. Mann (@Michael E. Mann)1484780151.0
In Texas, Dallas-Fort Worth recorded its last freezing temperature on Jan. 8. With no freezes expected into at least the last week of the month, there's a chance that the Jan. 8 reading of 20 degrees F will be Dallas-Fort Worth's last freeze of the winter. That would eclipse the earliest final freeze of the season (Feb. 5, 2000), in records extending back to 1899. The February warmth comes after a three-month span that was milder in Texas than any Nov/Dec/Jan period since the 1930s Dust Bowl, according to state climatologist John Nielsen-Gammon.
The warm, moist air prevailing along the South has been teaming up with occasional jet-stream intrusions to produce severe thunderstorms, including an unusually large number of tornadoes for the year thus far. This includes six confirmed tornadoes across southeast Louisiana on Feb. 7, with an EF3 twister causing more than 30 injuries and damaging or destroying more than 600 homes in and near East New Orleans (see the detailed National Weather Service survey report on all six tornadoes).
As of Feb. 13, theNational Oceanic and Atmospheric Administration's (NOAA) Storm Prediction Center (SPC) had tallied 163 U.S. tornadoes for the year thus far, not quite a record but far above average. On Tuesday morning, NOAA/SPC placed parts of the western and central Gulf Coast under a slight risk of severe weather, with a small enhanced-risk area along the central Texas coast near a large thunderstorm complex that had already produced several tornado reports west of Houston.
Close to the Century Mark in Oklahoma
While there's been quite a few ups and downs to the national temperature picture in recent days, with frequent frontal passages, the low temperatures haven't been all that low and the highs have been unusually high, as noted by Weather Underground blogger Steve Gregory. For the month to date through Feb. 12, NOAA had compiled a preliminary total of 1,207 daily record highs and 10 daily record lows, for a staggering ratio of more than 100 to 1. It's a picture in line with recent months: November 2016 had the largest ratio of record highs to lows of any month in modern records. It's also consistent with the inexorable effect of human-produced greenhouse gases in boosting temperatures to make record warmth more widespread and extreme than record cold.
One especially strong pulse of warm air jet pushed across the Southern Rockies and into the South from Friday into Sunday. As the already-mild air descended the Rockies, it warmed further due to downslope compression, leading to some eye-popping readings. Several stations in southwest Oklahoma soared into the upper 90s on Saturday. The town of Magnum hit an astounding-for-February 99°F, which tied the state record for any winter month (Dec/Jan/Feb) that was set at Arapaho on Feb. 24, 1918.
Here's a sampling of the all-time February heat records set over the past several days. In many cases, you have to go to mid-March to find comparable warmth!
Friday 2/10:
Wichita Falls, Texas: 94°F (next-earliest reading at least this warm was 98°F on 3/1/2006; records began in 1923)
Liberal, Kansas: 90°F (next-earliest 90° was 3/11/1989; records began in 1893)
Amarillo, Texas: 89°F (next-earliest 89° was 3/10/1989; records began in 1892)
Goodland, Kansas: 87°F (next-earliest 87 was 3/10/1989; records began in 1895)
Denver, Colorado: 80°F (next-earliest reading at least this warm was 81°F on 3/16/2015; records began in 1872). A cooperative observing station at the site of Denver's former Stapleton Airport, where official readings were taken until the mid-1990s, reported 83°F.
Saturday 2/11:
Lubbock, Texas: 91°F (next-earliest reading at least this warm was 95°F on 3/11/1989; records began in 1911)
Sunday 2/12:
Norfolk, Virginia : 82°F (ties all-time monthly high set on 2/4/1890 and other dates; records began in 1874)
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By Bob Henson
After the least-deadly year for U.S. tornadoes in three decades, 2017 is off to a troublesome start. At least 19 people died over the weekend in two consecutive nights of tornadoes across the Deep South, compared to the total of 17 fatalities recorded for the entire year of 2016. Although midwinter outbreaks don't happen every year in the U.S., they're most likely to be across the South when they do occur. Many of the deadliest tornadoes in these outbreaks happen overnight, when residents may be caught asleep or otherwise unaware and when getting to shelter can be difficult. The high proportion of manufactured/mobile homes across the South adds to the vulnerability of residents.
This past weekend's activity was fed by a powerful disturbance rolling through the polar jet stream atop very sultry air for midwinter at ground level. Jacksonville, Florida, set a record high of 84 F on Saturday and air with dew points well above 70 F streamed onshore through the weekend.
The severe weather occurred in three distinct rounds, as shown in the satellite loop embedded at bottom.
6 Weather Predictions for 2017 https://t.co/zGW4s21KcT @BraveNewClimate @WarmingGlobeHub— EcoWatch (@EcoWatch)1483319706.0
A pre-dawn supercell tore across southeast Mississippi and southwest Alabama early Saturday. Five tornadoes were reported. The most extensive damage occurred in and near Hattiesburg, Mississippi, around 4:00 a.m. CST by a long-track tornado (31 miles), a half-mile wide at its peak, that was rated EF3 on the enhanced Fujita intensity scale. This tornado produced 4 deaths and 56 injuries, according to the National Weather Service office in Jackson, Mississippi. Insured damages are likely to top $200 million in Hattiesburg alone, Insurance Commissioner Mike Chaney said. Just four years ago, on Feb. 10, 2013, Hattiesburg was extensively damaged by an EF4 twister that caused more than 80 injuries in two counties.
A wide shot of all the homes damaged looking towards Edwards Street in downtown Hattiesburg. https://t.co/elmJ2hA10c— Ryan Moore (@Ryan Moore)1485017808.0
A more extended, widespread round of 31 tornadoes occurred from midday Saturday into Sunday morning. The main culprits were two long-lived supercell storms, the first of which rolled from extreme eastern Alabama across central Georgia to extreme western South Carolina from about 10 a.m. to 4 p.m. EST. The second supercell tore across southern Georgia after midnight. Eight people were killed when a tornado ripped through a mobile home park southeast of Adel, Georgia, around 3:45 a.m. EST Sunday. Two others died in the same storm a few minutes later.
Conditions became increasingly volatile by midday Sunday, leading the National Oceanic and Atmospheric Administration (NOAA) Storm Prediction Center to issue a rare "high risk" outlook (its first anywhere since 2014) for parts of southeast Georgia and northern Florida. Instability was more than adequate for severe weather and wind shear was at extreme levels, with very high storm helicity (the amount of rotation imparted to a storm by winds at various levels). By early afternoon, thunderstorms were sweeping from the Gulf of Mexico into the Florida Panhandle with well-developed rotation evident on radar, a rare occurrence along this coast. The worst storm of the day produced a tornado that ravaged a mobile home park in Albany, Georgia, killing at least 4 people.
The afternoon's other thunderstorms developed so quickly and vigorously that they competed with each other, reducing the odds that another long-lived tornadic supercell would emerge. Four other tornadoes were reported on Sunday afternoon and evening, but none of them produced widespread destruction.
A Noteworthy January for Tornadoes
All told, NOAA/SPC logged more than 40 tornado reports from early Saturday through early Monday, scattered from western Louisiana to far southeast Georgia. Loosely speaking, this whole event might be considered a single outbreak, since it emerged from the same overall weather pattern. However, experts often define an outbreak as a string of tornadoes with no more than six hours of tornado-free conditions. By that standard, we could label the early-Sunday tornadoes (round #2 above) as an "outbreak" and all three periods above as a "sequence."
Only a few Januarys since 1950 have produced outbreaks or sequences topping this one, according to a compilation from ustornadoes.com. The reigning champion is the outbreak of Jan. 21-23, 1999, which led to nine deaths and produced 129 tornadoes from east Texas to southern Illinois. There was one F4 tornado in that event in far northeast Arkansas and 11 other tornadoes were given F3 ratings on the original Fujita tornado intensity scale that was in use at the time.
The nation's deadliest individual tornadoes on record in January, as noted by weather.com, were two Arkansas twisters that each led to 55 fatalities: one in Fort Smith on Jan. 11, 1898 and the other in Warren on Jan. 3, 1949.
Echoes of Another El-Niño-to-La-Niña Winter
Through early Monday, the Storm Prediction Center had logged a total of 91 preliminary tornado reports for the month so far. The upcoming pattern will be much less conducive to severe weather throughout the week and perhaps all the way to the end of the month. Even so, if all or most of these reports are confirmed, this could end up as the second most active January for tornadoes since comprehensive records began in 1950, according to ustornadoes.com. The clear record-holder is January 1999, when a total of 212 tornadoes were notched.
Interestingly, the twister-packed January of 1999 occurred during a moderately strong La Niña event that was in place one year after the record-setting 1997-98 El Niño event. Similarly, we're now one year past the comparably strong 2015-16 El Niño event and again experiencing La Niña, albeit a weak one. The only other "super El Niño" on par with these was in 1982-83; the following January of 1984 was very quiet tornado-wise, with only one confirmed twister. That year as a whole was quite active, though, with a devastating tornado outbreak in the Carolinas on March 28, 1984, killing 57 people and injuring more than 1000. In general, La Niña years appear to be a bit more favorable than El Niño years for early-spring tornado outbreaks, but this applies mainly to La Niña events that are at least moderately strong, which the current one isn't. Recent work led by John Allen (now at Central Michigan University) has bolstered the idea that La Niña is more favorable than El Niño for springtime hailstorms and tornadoes.
2-day GOES IR loop of severe thunderstorm evolution across southeast US. #alwx #gawx #flwx https://t.co/SODXiGe2kh— Bill Line (@Bill Line)1485130559.0
Reposted with permission from our media associate Weather Underground.