B. Precipitation (Rain & Rainshowers) Description
1. Rains
- Overcast sky with continuous or steady precipitation that may last several hours.
- Has a water droplets of 0.5 mm or greater in size but if widely scattered the drops may be smaller.
- Associated with meso-scale (synoptic) system or macro-scale (large scale) system like TC's, Easterly Waves, Monsoons, Fronts and ITCZ.
RAIN CLASSIFICATION | DEFINITION/DESCRIPTION |
Very Light Rains
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- Scattered drops that do not completely wet an exposed surface regardless of duration.
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Light Rains
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- The rate of fall is from trace to 2.5 mm per hour.
- Individual drops easily identified and puddles(small muddy pools) form slowly.
- Small streams may flow in gutters.
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Moderate Rains
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- The rate of fall is between 2.5 mm to 7.5 mm per hour.
- Puddles rapidly forming and down pipes flowing freely.
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Heavy Rains
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- The rate of fall is greater than 7.5 mm per hour.
- The sky is overcast, there is a continuous precipitation.
- Falls in sheets, misty spray over hard surfaces.
- May cause roaring noise on roofs.
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Monsoon Rains
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Other Descriptions:
- Heavy and continuous precipitation attributed to either the Southwest or Northeast Monsoon.
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Occasional Rains
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- Not frequent but is recurrent precipitation.
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Widespread Rains
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- Precipitation occuring extensively throughout an area.
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Frequent rains
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- Precipitation occuring regularly and often throughout the time duration.
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Intermittent Rains
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- Precipitation which ceases at times and re-occur again.
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2. Rainshowers
- Precipitation of short duration but usually of greater intensity from convective clouds(primarily cumulus or cumulonimbus)
- Characterized by sudden start and sudden end of precipitation, rapid change in intensity.
RAINSHOWERS | DEFINITION/DESCRIPTION |
Scattered Rainshowers
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- The rain-bearing clouds is distributed spatially resulting to rainshowers occuring to the bigger part of the forecasted area.
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Isolated Rainshowers
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- The rain-bearing clouds is small and isolated resulting to rainshowers occuring only to a small part of the forecasted area.
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Occasional Rainshowers
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- There is a large amount of convective clouds and precipitation occur in most parts of the forecasted area occasionally, and varying in rainfall amount.
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Squally Rainshowers
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- Showers accompanied by brief but sudden strong or gale force winds.
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C. Wind Description(Based from the Beaufort Wind Scale and the Saffir-Simpson Scale)
WIND DESCRIPTION
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UNITS in KPH
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UNITS in KNOTS
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DESCRIPTION AS OBSERVED
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Light Winds
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19 or less
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10 or less
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- Wind felt on face.
- Ordinary wind vanes moved by wind.
- Leaves rustle.
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Moderate Winds
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20-29
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11-16
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- Wind raises dust and loose paper.
- Small branches are moved.
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Moderate to Occasionally Strong
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- Moderate winds mostly persist but there are instances during the forecast period that it reaches strong wind force.
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Fresh Winds*
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30-39
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17-21
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- Small trees in leaf begin to sway.
- Crested wavelets appear on inland waters.
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Strong Winds |
40-50 |
22-27 |
- Large branches in motion.
- Whistling heard in telephone wires.
- Umbrellas used with difficulty.
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Gale:
1 Near Gale* 2 Gale 3 Strong Gale*
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51-62 63-75 76-87
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28-33 34-40 41-47
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- Whole trees in motion.
- Inconvenience felt when walking against wind.
- Twigs break off road.
- Cars veer on road.
- Larger branches break off.
- Slight structural damade occurs-roofing dislodged.
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Stormy:
1 Storm
2 Violent Storm*
3 Typhoon*
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88-102
103-117
118 or more
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48-55
53-63
64 or more
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- Trees uprooted.
- Considerable structural damage.
- Widespread damage.
- Widespread damage.
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- *Terms that are not normally used by meteorological centers in forecasts formulation and communication
- Gust - any sudden brief increase of wind speed usually less than 20 seconds followed by a lull or slackening in wind speed
D. Sea Condition as affected by Wind Force (Based from the Beaufort Wind Scale)
WIND FORCE | UNITS in (MPS) | UNITS in (KTS) | WAVE HT.(METERS) | SEA CONDITION |
Calm |
0-1.5 |
0-3.0 |
0.1 |
- Ripples with the appearance of scales are formed but without foam crests.
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Smooth |
1.5-4.0 |
3.0-8.0 |
0.1-0.5 |
- Small wavelets, still short but more pronounced.
- Crest have glassy appearance and do not break.
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Slight |
4.0-8.0 |
8.0-16.0 |
0.5-1.25 |
- Small waves, becoming longer.
- Fairly frequent white horses.
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Moderate |
8.0-11.0 |
16.0-22.0 |
1.25-2.5 |
- Moderate waves taking a more pronounced long form.
- Many white horses are formed-a change of some spray.
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Rough |
11.0-16.0 |
22.0-32.0 |
2.5-4.0 |
- Large waves begin to form.
- Sea heaps up and white foam from breaking waves begin to be blown in streaks along the direction of wind.
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Very Rough |
16.0-20.0 |
32.0-40.0 |
4.0-6.0 |
- Moderately high waves of greater length.
- Edges of crest begin to break into spindrift.
- Foam is blown in well-mark streaks along the direction of the wind.
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High |
20.0-26.0 |
40.0-52.0 |
6.0-9.0 |
- High to very high waves with long overhanging crests.
- The surface of the sea takes on white appearance.
- The thumbling of the sea becomes heavy with visibility affected.
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Very High |
26.0-34.0 |
52.0-68.0 |
9.0-14.0 |
- Exeptionally high waves.
- Small and medium size ships occasionally lost from view behind waves.
- The sea is completely covered with long white patches of foam.
- The edges of wave crest are blown into froth.
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Phenomenal |
>34.0 |
>68.0 |
>14.0 |
- The air is completely filled with foam and spray.
- Sea completely white with driving spray.
- Visibility very seriously affected.
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