Atlantic Hurricane Activity 2007. 2 Composites of the WH Warm Pool (1950-2000) Interannual variability of the AWP is large Large AWPs are almost three.

AtlanticHurricaneActivity2007

2

Composites of the WH Warm Pool (1950-2000)

Interannual variability of the AWP is large Large AWPs are almost three times larger than small ones

5 Largest WPs 5 Smallest WPs

Dark contour ==> SST = 28.5°C

3

The warm pool area follows closely the tropical North Atlantic SST Interannual variability is large, some related to Pacific ENSO

Index of the WHWP

4

2 = 40% 2 = 95%

==> we need skillful numerical model

forecasts!!

5

54 Years of Atlantic Hurricanes (1950-2003)

Busy hurricane years

= years for which the number of late-season hurricanes fall within the top tercile of all years

Of the 18 years with small warm pools

3 busy years, 23 storms

Of the 18 years with large warm pools

11 busy years, 82 storms

6

ENSO: shear is increased but moist instability (CAPE)

also increases

Warm pool: moist instability (CAPE) and shear work

together

7

Summary of Summer Responses to AWP

8

Slight warming of IAS, normal SST over the TNA & MDR. Dry over Caribbean & ENP regions.

Warming in Gulf of Guinea implies a weak West African Monsoon, south-shifted ITCZ.

Tendency toward a negative North Atlantic tripole pattern.

North Atlantic: SST, SST Tendency, OLR, 850mb Wind8

9

Recent Evolution of Equatorial Pacific SST (shaded, ºC), Surface Zonal Wind (contour, m/s) and Upper Ocean (0-300m) Heat Content Anomaly (shaded, ºC) and MJO Activities

Since mid-May 2007, two oceanic Kevin wave episodes were evident in heat content (HC) anom., which have brought HC in the central-eastern Pacific from below-normal to near normal from May to June, and from near normal to below-normal from June to July. Corresponding to the recent negative HC surge , SST has transitioned from near normal to below-normal between 140W and 110W in mid-July. The intraseasonal variability in the ocean was apparently associated with the intraseasonal surface wind variability related to the Madden Julian Oscillation, which was represented by 200mb velocity potential anom.

9

10

CFS Nino3.4 Forecasts from Different Initial Months

Underestimated the amplitude of the 2006/07 El Nino.

Missed the fast termination of the 2006/07 El Nino.

Missed the onset of the 2006/07 El Nino.

Forecast La Nina to be developed during late summer to autumn of 2007.

10

But: Atlantic 2007 least active in 50 years!1) Weak West African monsoon2) Normal TNA SST (MDR)3) Weak and/or late La Niña4) AMO negative tendency

2007season

1452

67

2007 season ACE activity index