Colin arrives; extreme heat records fall for Ukraine and 5 U.S. cities

Tropical Storm Colin has made its debut over the Atlantic, but does not appear to be a threat to any land areas over the next five days. Satellite imagery shows that Colin is intensifying, as both the intensity and areal extent of heavy thunderstorms has increased over the past few hours. A respectable low-level spiral band is developing to the north of the center, and upper-level outflow is beginning to appear on all sides of the storm. Colin is a very small storm, and its tropical storm force winds extend out just 30 miles from the center. Colin passed about 50 miles south of Buoy 41041 early this morning, and generated top sustained winds of 27 mph at the buoy. There is some dry air associated with the Saharan Air Layer (SAL) to the northwest of Colin, but this dry air is not getting entrained into Colin at present. Wind shear is a low 5 - 10 knots and sea surface temperatures are a very warm 28 - 29°C, so continued development is likely today. The main negative for development appears to be the storm's small size, which makes it vulnerable to modest increases in wind shear or dry air entrainment. The first flight of the Hurricane Hunters into Colin is scheduled for Wednesday morning.


Figure 1. Morning satellite image of Tropical Storm Colin.

Forecast for Colin
The latest 6Z (2am EDT) models are fairly unified taking Colin to the west-northwest at 20 - 25 mph for the next three days. This would bring squalls from the storm's outer rainbands to the northern Lesser Antilles Islands, such as Antigua and Barbuda, by Wednesday afternoon. The center of Colin should pass to the northeast of the islands, and the storm is small enough that the islands are unlikely to experience tropical storm force winds. As Colin makes its closest approach to the Lesser Antilles on Wednesday night, the storm will begin to encounter strong upper-level westerly winds associated with the counter-clockwise flow of air around an upper-level low pressure system centered between Bermuda and Puerto Rico. The latest SHIPS model forecast predicts that these winds will cause wind shear to rise to the moderate level, 10 - 20 knots, by Wednesday morning, and to the high level, 20 - 30 knots, by Thursday. There is considerable dry air associated with the upper level low that should cause problems for Colin, as well. The high wind shear and dry air should weaken Colin. NHC is giving Colin a 25% chance of attaining hurricane status this week.

A trough of low pressure is expected to move off the U.S. East Coast on Friday, and this trough will pull Colin to the northwest and cause it to slow down on Wednesday. By Friday, Colin will be moving at half of its current speed. It is unclear if the trough of low pressure will be strong enough to fully recurve Colin out to sea late this week. Some of the models predict Colin will not recurve out to sea, and that high pressure will build back in this weekend, forcing Colin towards the U.S. East Coast. A second trough of low pressure is predicted to move off the U.S. East Coast next Monday, so Colin will have a second opportunity to recurve out to sea then. It is possible that Colin could make landfall along the U.S. East Coast or in the Canadian Maritime provinces 7 - 10 days from now, though it is still too early to assess the risk of this happening, nor how strong Colin might be.

Ukraine ties its record for hottest temperature in history
On August 1, Ukraine tied its record for hottest temperature in its history when the mercury hit 41.3°C (106.3°F) at Lukhansk. The Ukraine also reached 41.3°C on July 20 and 21, 2007, at Voznesensk. Sixteen of 225 nations on Earth have set extreme highest temperature in history records this year, the most of any year. The year 2007 is in second place, with fifteen such records.

Five major U.S. cities record their warmest month in history during July
July 2010 was the warmest month in history for five U.S. cities:

Las Vegas, NV: 96.2°F (old record: 95.3°F, July 2005).
Atlantic City, NJ: 79.8°F (old record: 78.7°F, July 1983)
Washington, D.C.: 83.1°F (tied with July 1993)
Baltimore, MD: 81.5°F (tied with July 1995)
Trenton, NJ: 80.5°F (tied with July 1955)

Also, in June, Miami, FL recorded its warmest month in history: 85.6°F (old record: 85.4°F in June 1998.)

Commentary
None of the 303 major U.S. cities listed in the records section of Chris Burt's book Extreme Weather has set a coldest month in history record since 1994 (these 303 cites were selected to represent a broad spectrum of U.S. climate zones, are not all big cities, have a good range of elevations, and in most cases have data going back to the 1880s.) There were just three such records (1% of the 303 major U.S. cities) set in the past twenty years, 1991 - 2010. In contrast, 97 out of 303 major U.S. cities (32%) set records for their warmest month in history during the past twenty years. It is much harder to set a coldest month in history record than a coldest day in history record in a warming climate, since it requires cold for an extended period of time--not just a sudden extreme cold snap.

Are the pattern of U.S. temperature records due to the Urban Heat Island effect?
Is the huge disparity between extreme heat records and extreme cold records in the U.S. due to global warming, or the Urban Heat Island effect? The Urban Heat Island (UHI) effect occurs when development of former natural areas into pavement and buildings allows more heat to be trapped in cities, particularly at night. During the day, the UHI effect often leads to a slight cooling, since it can increase the amount of turbulence, allowing cooler air to get mixed down to the surface. For example, Moreno-Garcia (1994) found that Barcelona, Spain was 0.2°C cooler for daily maxima and 2.9°C warmer for minima than a nearby rural station.

However, temperature records are typically taken in parks and airports removed from the main heat-trapping areas of cities, and are not as strongly affected as one might expect. There are several reasons for this. One is that when tall buildings are present, they tend to block the view to the sky, meaning that not as much heat can escape upwards. In addition, the presence of moist vegetation keeps the atmosphere moister in park-like areas (which include the grassy fields near airports where temperature measurements are taken). This extra moisture helps cool the atmosphere on a local scale of tens of meters, due to latent heat effects (the energy required to convert liquid water to water vapor). Peterson (2003) found that "Contrary to generally accepted wisdom, no statistically significant impact of urbanization could be found in annual temperatures." The study used satellite-based night-light detection to identify urban areas. Recent research by Spronken-Smith and Oke (1998) concluded that there was a marked park cool island effect within the Urban Heat Island. They found that parks in typical cities in the U.S. have temperatures 1 - 2°C cooler than the surrounding city--and sometimes more than 5°C cooler. While the Urban Heat Island effect probably has contributed to some of the reduction in record low temperatures in the U.S. in the past decade, research by Parker (2004, 2006) and Peterson (2003) theorizes that Urban Heat Island effect is a factor ten or more less important than rising temperatures due to global warming.

Chris Burt wrote me yesterday about Las Vegas' all-time warmest month record set in July. He noted that none of the sites nearby Las Vegas' McCarran Airport (where the official obs are kept) came close to setting a warmest month in history record. McCarran Airport has set new warmest month in history records in 2003, 2005, and now 2010. These two facts make us suspect that in the case of Las Vegas, an urban heat island effect may be contributing to the spate of recent warmest month in history records there. The heat records for Atlantic City, Washington D.C., Baltimore, and Trenton do not appear to have as much of a UHI influence, since record highs were set over such a large area of the mid-Atlantic in July.

Is the Urban Heat Island effect partially responsible for global warming?
Global warming is affecting the entire Earth, including rural areas far from cities, and the 70% of the world covered by ocean. Thus, the Urban Heat Island effect--if not corrected for--can cause only a small impact on the global temperature figures. Since the Urban Heat Island is corrected for, the impact on the observed global warming signal should be negligible. For instance, NASA uses satellite-derived night light observations to classify stations as rural and urban and corrects the urban stations so that they match the trends from the rural stations before gridding the data. Other techniques (such as correcting for population growth) have also been used. Despite these corrections, and the fact that the Urban Heat Island effect impacts only a relatively small portion of the globe, global warming skeptics have persistently used the Urban Heat Island effect to attack the validity of global warming. There are no published peer-reviewed scientific studies that support these attacks.

References
Parker, D.E., 2004, "Large-Scale Warming is not Urban", Nature 432, 290, doi:10.1038/432290a, 2004.

Parker, D.E., 2006, "A Demonstration that Large-Scale Warming is not Urban", J. Climate 19, pp2882-2986, 2006.

Peterson, T.C., "Assessment of urban versus rural in situ surface temperatures in the contiguous United States: No difference found", Journal of Climate, 16, 2941-2959, 2003.

Spronken-Smith, R. A., and T. R. Oke, 1998: "The thermal regime of urban parks in two cities with different summer climates. Int. J. Remote Sens., 19, 20852104.

The surface temperature record and the urban heat island, realclimate.org post, 2004.

Next update
I have a series of meetings today that will probably keep me from making another post, and keep me from doing my weekly Internet radio show, Hurricane Haven. I'll be back Wednesday morning, at the latest, with a new post.

Jeff Masters