The current system that brought Alvarenga to Ebon rather than to another atoll, or to no atoll at all, is not fully resolved by the oceanographic models. The models show that objects starting from that departure point cluster in the general region of the Marshall Islands after approximately 14 to 20 months. They do not predict exactly which atoll an object will reach, because the specific path depends on the specific conditions during the specific period of the drift — conditions that vary and that the model captures in aggregate rather than precisely.
What the models do show is that Ebon Atoll’s position — southernmost in the chain, exposed to the main westward-flowing current before that current is deflected by the island arc — makes it a likely landfall for objects coming from the east. Objects that hit the chain tend to hit its southern end first, because that is where the current is least deflected. If Alvarenga was going to reach any part of the Marshall Islands, Ebon was among the most probable destinations.
This is not to say his landfall was predetermined; small variations in current and wind could have sent him south of the chain into open water, which extends all the way to Micronesia and beyond. The Eneaitok islet he reached — part of the outer ring of Ebon Atoll — was inhabited by exactly two people, Amy Libokmeto and Russell Laijedrik. If he had reached an adjacent uninhabited islet, the boat might have grounded on a reef and he might not have survived the landing. If he had reached a slightly different part of the atoll’s outer ring, there would have been no one to find him.