July 17, 2000
Weather Synopsis...
A trof of low pressure extended from NW Quebec down across the offshore waters.
Seabreeze Analysis...
The radar image below is in precipitation mode and does not show the seabreeze front at all.
The radial velocity image does a somewhat better job of showing the seabreeze front on this day. Notice the area of green right along the Ocean County coastline, as well as some scattered green in the Atlantic City area. This is indicative of winds blowing towards the radar site at Ft. Dix.
Observations...
The wind direction graph from Avalon shows that winds were onshore during the morning and early afternoon, and then slowly shifted to a SW direction.
Model Discussion...
-MM5
The image below shows the winds and pressure valid for 15Z on July 17th. It shows a E to SE wind right along the coast, but a W to SW wind 50 miles inland.
The MM5 temperature image below shows a distinct temperature gradient right along the coast at 15Z indicative of a seabreeze.
Below is a meteogram produced by the MM5 model which shows hourly conditions at a single location, in this case Atlantic City. Look at the Lowest Model Level Winds (kt) on the right. It shows a NE wind in the morning shifting to a SE wind by 16Z, and then a S wind by 18Z.
Below is a Skew-T diagram forecast for Atlantic City. This shows a vertical profile of the atmosphere. On the left is a vertical profile of temperature (red) and dewpoint (green). In the middle is the wind speed and direction with height. For 15Z it shows an E wind at the surface and a W wind at the 800mb pressure level. This shows the vertical structure of the seabreeze circulation. An onshore wind at the surface and an offshore wind aloft.
-COAMPS
Below is the COAMPS forecast of wind and pressure for 18Z. It shows a light SSE wind for this time.
Below is the COAMPS forecast of temperature valid for the same time. A definite temperature gradient exists right along the coastline.
Below is the COAMPS forecast of Relative Humidity valid for 18Z. It shows a very sharp gradient in RH along the coast, with a reading of nearly 96% in Cape May and 60% in Philadelphia.
-NOGAPS
Below is the NOGAPS forecast for wind and pressure valid at 18Z. It shows no evidence of a seabreeze at all. It shows a SW wind across the entire region. A possible explanation for this is the coarse resolution of this model compared to the MM5 and COAMPS was not able to pick up on the very small scale of this seabreeze case.
Model Analysis- Of the three models profiled on this date, the MM5 and the COAMPS seemed best able to predict the seabreeze formation. The NOGAPS with its lower resolution was not able to pick up on this day due to the seabreeze's very small spatial and temporal scale.
SST Discussion...
Below is a graph of SST at the Atlantic City Marina. it shows a drop in temperature of several degrees Celcius early in the day followed by an almost equal increase in SST.
The SST image below shows some possible upwelling along the coast, particularly in the region of Seaside Heights and Toms River.
CODAR Information...
The ocean currents for this day began entirely offshore. As the seabreeze developed, one can see that the currents closest to shore slowly began to veer towards an onshore direction. By 1000Z the currents only near the A and B nodes had become onshore. By 1100Z the currents to the west of the halfway point of the N2, N1, and A lines had become onshore. By 1200Z the currents in the area of all five lines had become onshore. This slow progression to the east shows how the seabreeze circulation grows in scale and since the cell is symmetrical, the distance from the coastline to the edge of the circulation offshore is roughly equal to the distance between the coastline and and seabreeze front inland.
