ex-TD 5 regenerating; globe has 2nd or 5th warmest July on record

The remnants of Tropical Depression Five have emerged over the Gulf of Mexico, and the system has enough spin to regenerate into a tropical depression later today or early Tuesday. Latest long range radar out of Mobile, Alabama shows that a band of intense but disorganized thunderstorms lies over the northern Gulf of Mexico, and satellite imagery shows that this activity is intensifying and growing more organized. A center of circulation is becoming more defined about 60 miles southwest of Panama City, Florida. Strong upper-level winds out of the northeast are creating a moderate 10 - 20 knots of wind shear over ex-TD 5, and this shear is keeping heavy thunderstorms from forming on the northern side of the center of circulation. Thus, I expect that heavy thunderstorms will be slow to develop over land today. By Tuesday, ex-TD 5 should be able to intensify into a tropical depression or weak tropical storm with 40 - 45 mph winds, and heavy rains should spread across the entire Gulf Coast from central Louisiana to the Florida Panhandle. All of the models bring ex-TD 5 back ashore over Louisiana on Tuesday, and it is unlikely the storm will get sustained winds stronger than 50 mph. The GFDL model predicts ex-TD 5 will stay below tropical storm strength, while the HWRF predicts a 45-mph tropical storm at landfall on Tuesday. The Hurricane Hunters will fly into ex-TD 5 this afternoon to see if it has regenerated into a tropical depression. NHC is giving the system a 60% chance of developing into a tropical depression.


Figure 1. Morning satellite image of the remnants of TD 5.

Elsewhere in the tropics
All of the major models continue to predict a major pattern shift in the global atmospheric circulation late this week, which leads to breakdown of the Russian heat wave and start to the Cape Verdes hurricane season. Most of the models predict a tropical storm will form off the coast of Africa late this week, and track west-northwestward across the Atlantic. As usual, it is highly uncertain what track a storm that has yet to form might take.

The NOGAPS model is predicting the development of a strong tropical disturbance near the coast of Honduras late this week.

Smoke clears from Moscow
Moderate westerly winds over the past few hours have cleared Moscow's air, bringing an end to a 42-hour period where smoke from persistent wildfires blanketed the city. Temperatures at Moscow's Domodedovo airport hit 31°C (88°F) today, which is 11°C (20°F) above average. The latest forecast for Moscow calls continued very hot temperatures and light and variable winds through Wednesday, as Russia's record heat wave continues. However, on Thursday, a strong trough of low pressure is expected to move through European Russia, finally bringing an end to the Great Russian Heat Wave of 2010.


Figure 2. Departure of temperature from average for July, 2010. Image credit: National Climatic Data Center (NCDC).

Second or fifth warmest July on record for the globe
July 2010 was the second warmest July on record, behind 1998, according to the National Oceanic and Atmospheric Administration's (NOAA's) National Climatic Data Center (NCDC). July was the first month since February that was not the warmest on record. NASA's Goddard Institute for Space Studies rated July 2010 the fifth warmest July on record. Both NOAA and NASA rated the year-to-date period, January - July, as the warmest such period on record. July 2010 global ocean temperatures were the fifth warmest on record, while land temperatures were the warmest on record. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were the 2nd warmest on record in July, according to University of Alabama Huntsville (UAH), and the warmeest on record, according to Remote Sensing Systems (RSS).

For those interested, NCDC has a page of notable weather highlights from July 2010.

Russia, Finland, and Qatar set all time heat records
Three nations--Russia, Finland, and Qatar--recorded their hottest temperatures in history during July 2010. No nation set a coldest temperature of all time record.

Finland recorded its hottest temperature on July 29, 2010, when the mercury hit 99°F (37.2°C) at Joensuu. The old (undisputed) record was 95°F (35°C) at Jyvaskyla on July 9, 1914.

Qatar had its hottest temperature in history on July 14, 2010, when the mercury hit 50.4°C (122.7°F) at Doha Airport.

Russia had its hottest temperature in history on July 11, when the mercury rose to 44.0°C (111.2°F) in Yashkul, Kalmykia Republic, in the European portion of Russia near the Kazakhstan border. The previous hottest temperature in Russia (not including the former Soviet republics) was the 43.8°C (110.8°F) reading measured at Alexander Gaj, Kalmykia Republic, on August 6, 1940. The remarkable heat in Russia this year has not been limited just to the European portion of the country--the Asian portion of Russia also recorded its hottest temperature in history this year, a 42.7°C (108.9°F) reading at Kara, in the Chita Republic on June 24. The 42.3°C (108.1°F) reading on June 25 at Belogorsk, near the Amur River border with China, also beat the old recrod for the Asian portion of Russia. The previous record for the Asian portion of Russia was 41.7°C (107.1°F) at Aksha on July 21, 2004.

All of these records are unofficial, and will need to be verified by the World Meteorological Organization (WMO.) The source for the previous all-time records listed here is the book Extreme Weather by Chris Burt.

Seventeenth warmest July on record for the U.S.
For the contiguous U.S., it was the 17th warmest July in the 116-year record, according to the National Climatic Data Center. The year-to-date period, January to July, was the 27th warmest such period on record. Two states, Delaware and Rhode Island, had their warmest July on record. Fourteen other states had a top-ten warmest July on record, including nearly every state on the Atlantic East Coast. No state recorded a top-ten coldest July.

U.S. precipitation
For the contiguous U.S., July 2010 ranked as the 36th wettest July in the 116-year record. Four states--Iowa, North Dakota, South Dakota, and Nebraska--had a top ten wettest July on record. Only Louisiana had a top-ten driest July on record.


Figure 3. The record-setting hailstone of July 23, 2010, that fell on Vivian, South Dakota. Image credit: National Weather Service, South Dakota.

Record hailstone falls in South Dakota
A severe storm on July 23rd dropped hundreds of massive hailstones on the small town of Vivian, South Dakota. Local reports stated that every house in Vivian sustained some type of hail damage. One of the stones collected broke the U.S. record not only for the largest hailstone (in diameter) but also the heaviest. The stone measured 8 inches (20.3 cm) in diameter, 18.5 inches (47.0 cm) in circumference, and weighed 1.9375 lbs (0.89 kg). It was also reported that the hailstone was originally much larger, but the freezer it was stored in lost power for about five to six hours and the person who collected it kept opening the freezer door to show friends and relatives. Even so, it smashed the previous hailstone record of 7 inches (17.8 cm) diameter, collected in southern Nebraska in June 2003. The world record for the heaviest hailstone belongs to Bangladesh, with a stone collected in April 1986 that weighed 2.25 lb (1.02 kg).

U.S. tornadoes
On July 25th, an EF-1 tornado touched down in Bronx County, New York, marking only the second ever recorded in the Bronx. On July 26th, an EF-3 tornado hit rural Sheridan County, Montana, killing two. This ties as the deadliest tornado in Montana history, and only the fourth EF-3 or stronger tornado ever observed in the state.

La Niña intensifies to moderate strength
The equatorial Eastern Pacific Ocean is now experiencing moderate La Niña conditions. Sea surface temperatures (SSTs) over the tropical Eastern Pacific in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", dropped to 1.1°C below average by August 16, according to NOAA.. The Australian Bureau of Meteorology put this number at 1.0°C below average (as of August 8.) Moderate La Niña conditions are defined as occurring when this number reaches 1.0°C below average. SSTs 1.5°C below average would qualify as strong La Niña conditions. La Niña conditions must be present for several months before this will be officially classified as a La Niña event, but it is highly likely that a full-fledged La Niña event lasting at least seven more months has arrived. We started out the year with a strong El Niño, so it may seem surprising that we have transitioned La Niña so quickly, However, historically, about 35 - 40% of El Niño events are followed by a La Niña within the same year.

It is well-known that both the number and intensity of hurricanes in the Atlantic tend to increase during La Niña events. However, as I discussed in a post in June, since 1995, neutral years (when neither an El Niño or La Niña are present) have had Atlantic hurricane activity equal to La Niña years. The last time we had a strong El Niño event followed by a La Niña event in the same year, in 1998, we had a Atlantic hurricane season 40% above average in activity, with 14 named storms, 10 hurricanes, and 3 intense hurricanes. The season was relatively late-starting, with only one named storm occurring before August 20. I'm thinking this year's season may be similar, though four or more intense hurricanes are a good bet due to the record warm SSTs.

Both El Niño and La Niña events have major impacts on regional and global weather patterns. For the remainder of August, we can expect La Niña to bring cloudier and wetter than average conditions to the Caribbean, but weather patterns over North America should not see much impact. Globally, La Niña conditions tend to cause a net cooling of surface temperatures. Thus, while the past twelve month period has been the warmest globally since record keeping began in 1880, the calendar year of 2010 will probably end up just shy of being classified as the warmest year ever.

July 2010 Arctic sea ice extent 2nd lowest on record
Northern Hemisphere sea ice extent in July 2010 was the second lowest in the 31-year satellite record, according to the National Snow and Ice Data Center. Relatively cool weather occurred this July in the Arctic, compared to 2007, when the record low was set. Ice volume was at a record low for July, though, according to University of Washington Polar Ice Center. On August 16, the fabled Northwest Passage was just a day or two from melting open, and will probably be open for navigation during most of late August and all of September.

Jeff Masters