The migration from the north to the south typically begins during the month of Mne and ends the following month of Eyimi. The return migration from the south to the north typically begins during Sruka and ends in Beyra.
Migrants typically travel in large groups for protection from wild monsters and bands of thieving raiders. Also, it is common for caravans to hire soldiers as security against such attacks.
Additionally, many Istrians make a living by ferrying migrants across the many oceans of Istria. Those who own ships can make several trips transporting travelers during the migration season.
Permanent cities near the equator, such as Glidden, benefit from having many diverse peoples travel through them during the migration and have become strong trading centers as a result.
During the Second and Third Ages, the great kingdoms built roads, established routes, and maintained the Great Migration.
However, since the fall of Nerath and the end of the Third Age, the Great Migration has become more dangerous than ever. There is no established order to protect or maintain the caravans, so each must fend for themselves. Usually this entails hiring mercenary guards and sellswords, though this can also be dangerous as some "guards" could be brigands in disguise waiting to take advantage of desperate migrants.
If life on the migration is tough, staying settled past the equator is nigh impossible. To be sure, there are settlements such as Tetuskf and Eilthyra which have the means to survive through the darkness, but these cities are extremely uncommon. Temperatures on the dark side of Istria reach well below freezing, blizzards regularly blast the landscape, total darkness feels like suffocating to those without darkvision, and the monsters begin to emerge.
Creatures who cannot abide the sunlight thrive on the dark side of Istria. They rise from the Underdark when the light is gone to feast on stragglers, raid the settlements, or gather materials that are rare underground. These denizens of the Underdark perform a "reverse migration" as they travel in the opposite direction as the surface migrants in their attempt to avoid the light.