Extratropical Highlights

  Table of Indices  (Table 3)

  Global Surface Temperature  E1

  Temperature Anomalies (Land Only)  E2

  Global Precipitation  E3

  Regional Precip Estimates (a)  E4

  Regional Precip Estimates (b)  E5

  U.S. Precipitation  E6

  Northern Hemisphere

  Southern Hemisphere

  Stratosphere

  Appendix 2: Additional Figures

Extratropical Highlights

SEPTEMBER 2008

1. Northern Hemisphere

The 500-hPa height pattern during September 2008 featured positive anomalies from northeastern Canada to Scandinavia, and over the high latitudes of the central North Pacific, and negative anomalies across southern Europe (Fig. E9). During September, surface temperatures were above average in much of eastern North America, western Scandinavia, and the Middle East, and below-average in the south-central U.S. (Fig. E1). Rainfall was above average in the central and eastern U.S. and Gulf Coast , and portions of southeastern Europe, and below average in Alaska , western Canada , Scandinavia, and northeastern Europe (Fig. E3)

a. North Pacific/ North America

The mean 500-hPa circulation during September featured a fairly non-descript pattern of above-average heights over eastern Canada . However, there was significant variability during the month in response to three U.S.   landfalling hurricanes, which included Major Hurricane Gustav in Louisiana, Hurricane Hanna in South Carolina, and Major Hurricane Ike in Texas. These combined systems contributed to above-average precipitation in the Midwest, Gulf Coast, and eastern U.S. Additionally, the mid-Atlantic and northeastern states experienced many days of heavy precipitation in association with a strong extratropical storm.

b. Europe

The 500-hPa circulation featured above-average heights across Scandinavia and below-average heights across southern Europe , in association with the positive phase of the NAO (Table E1). This marks a significant departure from the strong negative NAO pattern that prevailed during the past five months. Consistent with this change, northern Europe recorded average to below-average precipitation during September, while southern Europe recorded average to above-average precipitation (Figs. E3, E4).

  2. Southern Hemisphere

The 500-hPa height field during September featured an anomalous zonal wave-3 pattern, with above-average heights centered east of New Zealand, east of South America, and over the central Indian Ocean, and below-average heights over the high latitudes of the eastern South Pacific, and south of both Africa and Australia (Fig. E15). No significant temperature or precipitation anomalies were observed over the SH land masses in September.