From the patcher...

We are currently experiencing stability issues with the NA/EU data center Worlds due to congestion.

The issue is being addressed, and new updates will follow as additional information becomes available.

We apologize for any inconvenience this may cause.

[Date & Time]
From Aug. 30, 2013 17:16 (PDT)

[Details]
- Unable to log into the NA/EU data center Worlds.

[Affected Worlds]
Adamantoise
Balmung
Behemoth
Cactuar
Cerberus
Coeurl
Diabolos
Excalibur
Exodus
Faerie
Gilgamesh
Goblin
Hyperion
Lamia
Leviathan
Malboro
Midgardsormr
Moogle
Odin
Phoenix
Ragnarok
Sargatanas
Shiva
Siren
Ultros