Complex sentence: Under the influence of a high pressure system, Erika moved quickly westward and strengthened under favorable conditions and made landfall as a hurricane on northeastern Mexico on August 16, but quickly dissipated inland.
Split into simpler sentences: Under the influence of a high pressure system, Erika moved quickly westward and strengthened under favorable conditions. Erika made landfall as a hurricane on northeastern Mexico on August 16, and quickly dissipated inland.