Temperature
The mean of the highest air temperature recorded in Mumbai is 35° C in the months of March, April and May while the mean lowest is 16° C recorded in the month of January. Mean daily maximum and minimum temperatures are 31° C and 24° C respectively.

Relative humidity
Mean yearly relative humidity at 0830 hours is 77% while the same at 1730 hours is 71%. The monthly average is lowest in February (62%) and highest in July to September (85%).

Rainfall
The average yearly rainfall is about 2098 mm, of which 1965 mm (93.66%) occur during June to September. Usually maximum monthly rainfall occurs in July. The average monthly rainfall in July is 709 mm. There is practically no rainfall from December to April.

Cyclone
In general the west coast of India is less prone to cyclonic storms compared to the east coast. From the information reported by India Meteorological Department (IMD) a total of 1034 disturbances occurred in the Bay of Bengal during the period 1891 to 1970 of which 363 intensified to cyclonic storms, the rest being ‘depressions’. On an average the number of cyclonic disturbances per year during this period was about 13. However, if the data is updated to 1990, the number of cyclonic events per annum works out to be 16, varying from a minimum of 8 to a maximum of 18. It is observed from the tracks of the cyclones in the Arabian Sea from 1877 to 1992 that only 10 storms endangering the Mumbai coast have occurred in the above said period i.e. at a frequency of once in 12 years.

Visibility
Throughout the year visibility is good as the region has zero fog days and therefore there are no constraints to the navigation on this count.

Salinity
Amba River which carries considerable amount of storm water discharge meets the sea water near the proposed port area. The estuary is known to become fresh water in its upper reaches, despite the high tidal range at the Dharamtar Port.

Tides
The tides in the Mumbai region are of the semi-diurnal type i.e. characterised by occurrence of two High and two Low Waters every day. There is a marked inequality in the levels of the two low waters in a day.
Highest High Water Level observed at the Mumbai harbour is +5.38m CD.

Wind
The Ship observed wind data for a period of 65 years from 1921 to 1985 from the India Meteorological Department (IMD) for the area shows that west is the predominant wind direction and that the wind speed is less than 20 knots (10 m/s) for 94% of time.

Waves
ADCP was installed near outer approach channel wherein it was observed that the predominant direction of waves was from West within the sector 215° N to 300° N. The Significant Wave Height, Hs varies between a minima value of 0.58 m and a maxima value of 4.93 m with the mean value being 1.4 m. The duration, Tp of the waves recorded was varying between 4.2 to 14.8 seconds with the average being 6.7 seconds. At the entrance to the outer approach channel, wave heights are less than 1 m, 2 m, 3 m, 3.5 m and 4 m in height for 15, 43, 89.6, 97.6 and 99.9% of the time respectively. However, due to attenuation, waves are well within acceptable limits in the Dock area.

Currents
The currents in the Mumbai region in the near shore zone are tide induced with reversal at high and low waters. The current strengths are of order of 0.4 m/s to 1.7 m/s (0.8 to 3.4 Knots). The currents in the creeks are also affected by the freshets which result in not only increasing the strength of the ebb current but also limiting the propagation of the tide upstream.

Sediment Transport
The West coast exhibits very low rates of “Littoral Drift” generated by wave action. Inside the Mumbai Harbour and the various creeks such as Panvel and Dharamtar, sediment transport is a tidal current induced phenomenon. Amba River which carries freshet discharges from its catchment area also brings silt from the upstream areas during ebb tides. Similarly, during the flood tide the currents would carry silt from the offshore up the estuary.