Whether or not you can apply overseas is subject to some debate; some think you can (as long as your current AP is still valid) while others think you cannot. However - even if the new one gets approved, you must return to the US before your old one expires. You can then use the new one to travel again. So regardless of whether or not you apply from overseas, you must still return to the US before your current one expires even if the new one is approved and waiting.