July 8, 2000
Weather Synopsis...
A 1024 mb high was located over western PA. The synoptic flow flow this feature was from the north. The afternoon seabreeze developed around 17Z as a SE wind developed along the coast.
Seabreeze Analysis...
Analysis of Observations...
The graph of temperature below shows a distinct temp drop around 17Z from 23C to 20C.
The graph of relative humidity shows a very remarkable drop in humidity, followed by an impressive 30% increase in humidity as the sea breeze front passes around 17Z.
The graph of wind direction shows that through much of the day winds were from the north, but then aound 17Z winds shifted to the SE and remained there through the rest of the evening.
Wind speed data shows that there is a local minimum in wind speed around the time of seabreeze frontal passage, then winds increased to around 8 m/s.
Mesoscale Model Discussion...
-MM5
The next few images are the MM5 mesoscale model forecasts at 4 km resolution for 15Z, 18Z, 21Z, and 0Z on July, 9. The 15Z forecast shows a N wind across the NJ shore. By 18Z the winds have shifted to an ESE wind direction at about 5 kts. By 18Z the forecasted wind direction was from the due south from 10 to 15 kts. A temperature gradient between the coast and the interior is well established by 18Z. By 0Z, the seabreeze front, indicated by the sharp temperature gradient, has moved well inland, especially so in Central NJ. At 0Z, the temperature over the land is cooler than the ocean, and as such a land breeze (offshore wind) appears to be developing.
SST Discussion...
The SST image from 2031Z below shows some cooler water right along the coast, but not much evidence of upwelling. A SST image from earlier in the day was unavailable due to cloud cover.
CODAR Information...
Below are CODAR plots from 10Z, 14Z, 16Z, 18Z, and 23Z.
At 10Z, the current offshore was to the SW, with velocities of 25-30 cm/s.
At 13Z, the current is still to the SW, however the velocity had decreased to only 15-25 cm/s.
At 14Z, the currents nearshore had become onshore, with velocities of 5-15 cm/s.
At 16Z the current field is almost entirely onshore, with velocites off of Brigantine between 25 and 30 cm/s.
At 18Z the currents were still onshore, but were directed more in a northerly direction. Velocities had decreased to 10-22 cm/s. This change in current direction is indicative of the winds over the coastal water becoming more southerly as the seabreeze circulation begings to break down offshore.
By 23Z the currents had almost all become offshore, as a land breeze takes over for the reasons discussed in the MM5 forecast analysis for 0Z on July 9.
