Body Blows to El Nino

A weak El Nino persists across the equatorial Eastern Pacific, but recent atmospheric processes have halted the expanse of warm sea surface temperature anomalies. 1 C anomalies now only exist along and south of the equator between 155 W and 103 W with a localized pocket of slightly higher anomalies (~1.5 C) between 130 W and 110 W. The 29 C isotherm that was located as far east as 165 W a couple of weeks ago has retreated to 175 W owing to anomalously strong trade winds just south of the equator. Furthermore, the very warm anomalies (3-3.5 C) located 50 to 75 meters below the ocean surface between 130 W and 100 W that were observed last week have since shrunk and decreased to 2-2.5 C. Needless to say, the current El Nino has taken some major body blows the last few weeks.




Global wind signals continue to suggest the former La Nina may be delivering the body blows. Since frictional torque spiked last week, it has since decreased and leveled off near climatology as strong high pressure centers near 45 N and S observed in early July have weakened. Mountain torque remains about a half standard deviation below climatology with positive contributions coming from South America and the tropics and negative contributions coming from Eastern Asia and North America. Relative AAM continues to remain flat lined near one half standard deviation below climatology, and the recent fluctuations of relative AAM tendency have caused the GWO to oscillate between phases 1 and 3.




Recent responses to these phases have been for a large anticyclone to be centered over the Desert Southwest while a very deep trough has dominated the Eastern U.S. Much warmer than normal temperatures have been experienced across the West, and record low temperatures have been broken in the Southeast. I expect this pattern will continue for a couple of more days before the trough lifts out of the Southeast and into the Ohio Valley. This will allow temperatures to warm back to normal for most locations in the South, but northwesterly flow aloft will lead to the formation of mesoscale convective complexes this week which will penetrate into the Deep South. I think our area should see near normal temperatures and slightly above normal rainfall for the upcoming week. By next weekend and extending into week 2, an unseasonably strong Aleutian low will significantly amplify the ridge across the West. At the same time, another trough should re-establish itself into the eastern half of the country. It appears that the coolest air will miss us to the east, but cooler than normal temperatures will likely dominate the first half of week 2 along with above normal precipitation. The second half of week two should see the trough lift and the upper flow flatten, which should allow for temperatures to warm near normal. The bottom line is that the worst of the heat should remain to our west through week 2.

Monsoonal convection remains in place across the Asia subcontinent and other tropical convection is occurring in Indonesia and the Western Pacific. This continues to be good news for these areas that desperately need rain, but Tropical Storm Molave brought substantial rains and flooding to Hong Kong. Competing tropical convective signals continue to add some uncertainty to the future weather and climate link. The two areas of convection are in the Indian Ocean centered near 60 E and another centered near 165 E and will be battling for supremacy. I think the convection in the Indian Ocean should begin to fade in the next month, but the convection in the equatorial Western Pacific will likely only become stronger. At that point, I believe we should begin to see the ocean and atmosphere become more synced.