The geomagnetic storm would happen globally. The magnetic field funnels the particles in at the poles, hitting both hemispheres simultaneously-- This means that the electromagnetic flux exerted from the ionosphere being excited would be global, with epicenters at the polar regions. Not the day side.
Also, the shielding is not what is the issue. The issue is that the transformers are connected to miles and miles and miles of conductor, which will resonate with the EM flux of the ionosphere during the event-- EG, many millions of volts of electrical potential oscillating at a low frequency outside the normal operating band of the transformer. This will damage/destroy the transformer.
Transformers locked in storage may be OK, but ones in active service will be connected to the power grid, which is what causes the above problem. There are not enough transformers stockpiled to replace all of them in an expedient manner. This means that the "aftermath" of such a calamity will have certain areas getting power, and others not, and subsequent riots, looting, and pilfering of functional transformers, resulting in inefficient and unpredictable power grid behavior in the years afterwards, and the logistical difficulties of manufacturing additional replacement units while this is all going on. At CURRENT levels of manufacture, it would take about 50 years to manufacture (I think that's right...) enough to rebuild the US's power grid. (let alone the world's!) A LOT CAN HAPPEN IN 50 years.
During that time, you would have many billions of people that were previously sustained by the abundance of electrical energy now suddenly thrust into a pre-electrical revolution setting. In the first year after the event, the lack of air conditioning alone would kill untold numbers. The lack of refrigeration would result in absurd numbers of people dieing of starvation, and the radical decline in hospital quality that lack of electrical power would induce would also come to bear.
This isn't something to joke about.