What occurs at $61.5^ ext{circ}$ latitude if the Moon reaches its most northerly point of $+28.5^ ext{circ}$ declination when viewed from the south?

It will just graze the horizon without rising above it.

The latitude of $61.5^ ext{circ}$ is mathematically significant because it is calculated as $90^ ext{deg} - 28.5^ ext{deg}$, where $28.5^ ext{deg}$ is the maximum northern declination the Moon achieves. If an observer is located exactly at $61.5^ ext{circ}$ latitude, and the Moon simultaneously reaches its extreme northerly declination of $+28.5^ ext{deg}$, the object's altitude above the horizon ($h = 90^ ext{deg} - | ext{latitude} - ext{declination}|$) equals zero. When this occurs, the Moon's highest point in its apparent arc places it precisely tangent to the horizon line—it grazes the horizon without clearing it to rise above, or it sets exactly upon reaching that extreme northern position, marking the precise boundary condition for guaranteed rise and set.