2015 Climate Summary of the Southeastern United States

Highlights

Following a record warm December, 2015 wrapped up with more abnormal climatic conditions. Nearly every state in the Southeast experienced much above normal temperature conditions (Fig. 1) and above average precipitation totals (Fig. 2). Florida, however, was around the precipitation average. Additionally, there were some significant climate anomalies throughout the year. A strong El Nino formed across the equatorial Pacific and peaked towards the end of the year. The North Atlantic hurricane season was slightly below average with 11 named storms, 4 hurricanes, and 2 major hurricanes. In October, Hurricane Joaquin interacted with an upper level low, which lead to historic rainfall amounts across the Carolinas. Around Charleston, South Carolina rainfall amounts were around 15-20 inches with isolated amounts of up to 25 inches. Severe weather swept across the south in late December, which caused tornadoes and record flooding. Lastly, Florida has its warmest year on record with an average statewide temperature of 3.3°F above normal.

Figure 1. Statewide average temperature ranks for January - December of 2015, Source: NOAA/NCEI

Figure 2. Statewide precipitation ranks for January - December of 2015, Source: NOAA/NCEI

Seasonal Analysis 

A prominent trough remained over much of the Southeast during the winter months. Consequently, most of the states experienced a below average winter, while Florida, Georgia, and South Carolina were around normal. Most of the lower Mississippi Valley experienced drier than normal conditions while the other Southeastern states were around normal precipitation totals for remainder of the winter season. 

By spring, the pattern shifted as most of the Southeast experienced above average temperatures and Florida set a new spring temperature record (4.6°F above average). Nighttime temperatures were much above normal, which allowed the average temperature to exceed above normal conditions. As for precipitation amounts, the southeast experienced a mix of climatic anomalies by the end of May. The lower Mississippi Valley had above normal precipitation amounts while Florida, North Carolina, and South Carolina experienced drier than normal conditions. The remaining Southeastern states were around their normal precipitation totals. Additionally, Tropical Storm Ana made landfall on May 10th near Myrtle Beach, South Carolina. Little damage was reported, but heavy rain fell across the Carolinas. 

Florida, Louisiana, North Carolina, and South Carolina experienced much above normal temperature conditions by the end of the summer. Kentucky and Tennessee remained around average temperatures by August while the rest of the Southeastern states were warmer than average. Below-average precipitation fell across the Southeast. Combined with warm temperatures, drought conditions worsened across the lower Mississippi Valley and Southeast. In contrast, above-average precipitation fell across Kentucky, Tennessee, and Virginia. In August, remnants of Tropical Storm Erika moved across Florida, which helped alleviate drought conditions. 

Every Southeastern state had an above-average fall temperature. Florida had its warmest fall on record with the statewide average around 3.6°F above the norm. As for precipitation, every state (except Florida) had above-average precipitation amounts by the end of fall. The historic flooding event in early October caused South Carolina to have its wettest fall on record with 23.76 inches (13.91 inches above average). Due to the rainfall, drought conditions improved across the entire Southeast.

Atlantic Hurricane Season 

Figure 3. 2015 Atlantic hurricane season with storm tracks and strength, source: NOAA National Hurricane Center

The 2015 Atlantic hurricane season had 11 named storms, 4 hurricanes, and 2 major hurricanes (Fig. 3). The season was slightly below the climatological mean. On average, 12.1 named storms occur with an average of 6.4 hurricanes and 2.7 major hurricanes. The lack of activity could be due to the El Nino, which tends to suppress Atlantic hurricane activity.

Two tropical storms made landfall (Ana and Bill) and no hurricane or major hurricane made landfall this season. Hurricane Joaquin did not make landfall; however, it did interact with an upper level low, which caused historic flooding in the Carolinas. This season continued the record-long streak of no major hurricane (category 3 and higher) making landfall. On average, a major hurricane makes landfall every 3 years. The last major hurricane to make landfall was Hurricane Wilma, which was November 24, 2005. 

Severe Weather Season

Figure 4. 2015 tornado occurrences in the United States, Source: NOAA Storm Prediction Center

For the United States, the preliminary report of tornadoes was around 1, 183. This season was below the climatological average, which is 1, 253 annually. Most months were around the climatological mean for tornado reports. However, May, November, and December were well above their respective averages. In May, there were 414 confirmed tornado reports, which is 138 above the average. In November, there were approximately 95 preliminary reports, which is 37 above the average. In December, there were 86 preliminary reports, which is 62 above average. Lastly, in the Southeastern U.S., there were no tornado reports, which was the first time that at least 1 tornado was not reported in the region. 

Reference: 

NOAA National Centers for Environmental Information, State of the Climate: National Overview for Annual 2015, published online January 2016, retrieved on January 28, 2016 from http://www.ncdc.noaa.gov/sotc/national/201513

Hurricane Patricia - One of the most powerful hurricanes on record.

At 12:00 UTC (8 a.m. EDT) on October 23rd, Hurricane Patricia became the most intense tropical cyclone in recorded history (globally) as it sustained wind speeds at 200 mph. Patricia grew from a tropical storm to a category 5 hurricane in 24 hours. Making Hurricane Patricia the greatest intensity rate (100 mb in 24 hours) in recorded history. When Hurricane Patricia intensified to 879 mb, it became the 5th most intense tropical cyclone in terms of minimum central pressure.

Satellite image of Hurricane Patricia 

Rapid Intensification 

The sea surface temperatures (SST) across the equatorial pacific have been above-normal for most of this year, indicating that El Nino conditions will likely occur during the 2015/2016 winter season. After Patricia organized, it propagated east/northeast over very warm SSTs. The environmental conditions were favorable for Patricia to intensify. There was very little wind shear, no dry air intrusion, and warm SSTs. The SSTs were around 30℃ (86℉). 

Sea surface temperatures across the equatorial pacific. source: http://www.ssd.noaa.gov/PS/TROP/DATA/RT/SST/PAC/20.jpg

Previous studies indicate that El Nino conditions can increase the likelihood of hurricane activity in the east Pacific ocean (Camargo et al. 2007). El Nino normally causes positive SST anomalies across the equatorial pacific as well as decreasing wind shear. However, the presence of El Nino was not the soul contributing factor to Hurricane Patricia's rapid intensification. For the past two years, there has been a consistent "blob" along the west coast of North America. The "blob" is a large area of above-normal SSTs, which might be in association with the Pacific Decadal Oscillation (PDO). Like the El Nino-Southern Oscillation (ENSO), the PDO goes through warm and cool phases. However, the PDO phases are every 20-30 years. Like ENSO, the PDO is in a warm phase, which is manifest with the above-normal SSTs along the pacific coast of North America. The combination of these two climate oscillations created favorable conditions for Hurricane Patricia to intensify rapidly. Additionally, with climate change, the ocean and atmospheric temperatures have increased, too. This combination of natural climate variability and climate change have increased the baseline temperature, which inherently allows the atmosphere to hold more water vapor. Therefore, there's more water available for tropical cyclones.

Satellite Movie Sees Record-Breaking Hurricane Patricia

Landfall
Patricia made landfall at approximately 7:15 p.m. EDT on Friday, October 23 near Cuixmal, Mexico as a category 5 hurricane. Which was only the second Pacific Hurricane on record to make landfall as a category 5. The maximum sustained wind speeds were 165 mph as it made landfall. This is the second most intense tropical cyclone to make landfall on record. Hurricane Patricia is behind Typhoon Haiyan, which made landfall with sustained winds of 174 mph.

What's in store for Patricia now?
Once Hurricane Patricia made landfall, it weakened to a tropical depression in 16 hours and combined with an upper-level low pressure system to cause rain across the southeast. The remnant of Patricia and the upper-level low caused extreme heavy rainfall over Texas, which caused more local flooding. Also, the combined systems are expected to continue across the southeast with the possibility of heavy rainfall and flash flooding.

24 hour total quantitative precipitation forecast. Source: http://www.wpc.ncep.noaa.gov/qpf/fill_94qwbg.gif?1445875070494

References:

Suzana J. Camargo, Kerry A. Emanuel, and Adam H. Sobel, 2007: Use of a Genesis Potential Index to Diagnose ENSO Effects on Tropical Cyclone Genesis. J. Climate, 20, 4819–4834.

doi: http://dx.doi.org/10.1175/JCLI4282.1