A student pilot aboard a C-150 was unable to maintain VMC on his first solo cross country.

Narrative

I was on my first solo cross-country flight to ITO around the north side of the island. I checked weather; radar; and satellite prior to departure. The weather appeared clear with high ceilings. As I came around Uppolu Point at 3;500 FT I could see that the northeast coast now had a low ceiling of about 2;000 FT. I descended and flew along the coast over the water because the terrain to my right was sea cliffs above 1;000 MSL. I got a report over CTAF from other traffic passing me the opposite direction (from ITO). The pilot report indicated some rain but ceilings no lower than 1;300 MSL. I descended below the ceiling and continued to monitor the visibility behind me in case I had to turn around. The ceiling kept coming down. When it got to 1;000 FT I decided to turn around.With terrain to my immediate right; dark clouds in front; ceiling at 1;000 and coming down I had very few options. I could have descended further but I was already in a descent and there was an updraft along the entire coast making it difficult to go down. I did not feel experienced enough to fly below 1;000 FT over the ocean so I decided to level off at 1;000 FT and turn around. I checked behind me and it looked clear so I started a turn to the left since there was terrain to my immediate right. Upon starting the standard rate turn to the left I entered a cloud. I managed to complete the 180 degree turn by instruments while still in the cloud. I held the new course and altitude until I saw a wisp of blue below me. I immediately slipped the plane down through the cloud and came out at about 800 MSL.The weather is variable here but my instructor had taken me on the same cross-country trip the day before and we had to fly over and under clouds and in rain along the coast. Had I not done the flight with my instructor the previous day I would have turned around much earlier. I got in trouble attempting to do the same thing I did the day before with my instructor. I did have a life vest.