The associations among peritraumatic posttraumatic stress symptoms (P-PTSS) in the immediate aftermath of trauma exposure, including those in the posttraumatic stress disorder clusters of intrusions, avoidance, negative cognitions and mood (NCM), and arousal, might indicate mechanisms through which enduring PTSD develops. During a period of war, exposed participants (N = 181) were sent twice-daily questionnaires for 30 days via smartphone. We repeatedly assessed the predictive associations between the P-PTSS clusters over time. We performed a multilevel pathway analysis built of multiple triple sequence responses (6,221 cases) on each of the four P-PTSS clusters at a mean time lag of 12 hr (Model A) and 24 hr (Model B) for 181 participants, 85 of whom had been diagnosed with a serious mental illness. Arousal predicted intrusion in Models A and B, bA = 0.08, 95% CI [0.03, 0.12], p < .001 and bB = 0.03, 95% CI [0.00, 0.07], p = .051, respectively; and NCM in Models A and B, bA = 0.09, 95% CI [0.05, 0.12], p < .001 and bB = 0.06, 95% CI [0.03, 0.09], p < .001, respectively. Intrusion predicted arousal in Model B, bB = 0.05, 95% CI [0.01, 0.08], p = .010. NCM predicted arousal, bA = 0.10, 95% CI [0.05, 0.14], p < .001, and avoidance bA = 0.05, 95% CI [0.00, 0.11], p = .052, in Model A. Avoidance did not predict any other cluster. Arousal seemed to be acting as a hub, strengthening feedback loops to and from NCM and intrusion.