‘Son of Juan’ Precipitation system that hit Nova Scotia 6 to 12 hours after Juan’s impact Produced more precipitation than that of Juan in Shearwater, NS (~30 mm)

Improved Guidance How much could have been done in real time at high resolution?

Change of North American flow at the DT from 21/00 to 23/12: The dominant broad trough in N. America is replaced by a primarily zonal flow, with a short wavelength ridge-trough couplet over eastern N. America. A warm anomaly travels across the continent, reinvigorated by convection, to amplify the eastern ridge. 21/00 23/12

0000 UTC, 24 Sept. 2003 Note the stationary warm ridge over Nova Scotia, polar jet at US-Canada border and ST jet over southern US

1200 UTC, 25 Sept. 2003 Short-wave ripples appear along the ST jet, as the midwestern trough digs southeastward

Note the reversal of the meridional PV gradient, indicating a barotropic instability

1200 UTC, 26 Sept. 2003

27/00; Son of Juan lies west of Florida; easternmost convection at 35 N, 65 W interacts with Juan

0000 UTC, 29 Sept. 2003 Both Juan and son of Juan accelerate poleward under the infliuence of the persistent, amplified ridge-trough couplet

1200 UTC, 29 Sept. 2003 Note Juan’s maintenance of its tropical characteristics, and that ‘Son of Juan’ helps to ‘protect’ Juan from the potentially cold air

‘Son of Juan’ Developed in association with a highly-amplified, persistent trough-ridge couplet Helped to protect Juan from extratropical influences as it traveled into the Maritime provinces Developed in a barotropically-unstable environment along the Gulf of Mexico coast of the US