Dear Friends,

 In May the six-month rainy season in northern Tanzania comes to an abrupt stop. A week later the grasses are dead on the southern grassland plains. The wildebeest freak out.

 The three months or so that the calves have had of endless, glorious grasses is over, and the calves are now strong. The rutting by the great males is done; most of the females are newly pregnant. What every wildebeest and zebra now need is food, new grass and it’s not on the southern plains where the herds have lingered since the new year.

 After frantic fighting and random running, the herds begin to gel into long files, sometimes 5-10 miles long, 4-5 abreast, and they begin running north.

 They run 4, 5, 6 hours without stopping. They stop only to drink or try to graze and during the night when they have to be specially concerned with predators. They will only stop running when they find new grass.

 Until now the rains have been pretty predictable, but as the season changes and the jet streams twirl backwards onto themselves and the monsoon prepares to alter, it’s never as clear where the rains will fall. Normally, they recede gradually towards Lake Victoria.

 So most of the herd begins to travel in that direction, northwest. But when an errant thunderstorm appears in the east, the herd fractures and some travel towards the clouds. When a leading file runs into prides of lion, they scatter and reform in multiple directions. When a mother loses her calve as she leaps over a croc in a raging river, she turns back.

 The uniformity of the great southern grassland herd is broken by events that become the most dramatic of the year. This is the “great run.”

 But exactly when and exactly where depend hugely on weather and a myriad of other wild events. To schedule definitely seeing this is as simple as specifically choosing the day in June that it won’t rain on your daughter’s wedding.

 I have a pretty good track record, probably better than anyone. My 40 years of guiding in the Serengeti gives me the depth of experience and patience to understand the signs. And this itinerary is my best shot in advance. Nevertheless, this is the least guaranteed of all four great migration safaris I’ll guide in 2014 of actually finding the great herds.

 But if we do, it can’t be topped. This is a great trip for veterans. It includes some of Tanzania’s finest and most luxurious camps. And it’s all game viewing, little else: six days alone in just the Serengeti.

 If you want to gamble on seeing the undisputed very most dramatic moments of the migration, this is the safari!

Jim Heck