chapter 5 summery Flashcards
surface charts include
- Four surface analysis per day transmited in two parts
- 00Z, 06Z, 12Z and 18Z
- Two daily 48-hour surface forecasts
- 00Z and 12Z
surface charts depict:
- Isobars
- Surface winds
- Frontal systems
- Low and high pressure center positions
- Central pressure
how is the leading edge of the ice depicted?
- It is depicted as black dots
- Found on the northern edge of the graphics
The 48 hour surface forecast displays
- The synoptic scale system’s position and central pressure in
- 24 hour track history
- 24 hour forecast position
Bold capital letters represent
- Systems having or expecting to have synoptic scale
- Gale
- Storm or
- Hurricane force conditions
- Significant weather systems have labels depicting whether the system has the above conditions as observed by
- Ships
- Buoy observations
- Remote sensing satellite data
- Computer model guidance
labels “developing gale”, “developing storm” or “developing hurricane force” are given to
- Systems expected to develop gale, storm or hurricane force conditions in 24 hours
the label “RAPIDLY INTENSIFYING” is given to
- Surface low pressure falls of 24 mb or greater during a 24 hour period
the surface charts generated for each ocean consist of:
- Isobaric pressure analysis at 4 mb contour interval spacing
- The central pressure mb values of low and high pressure systems
- Depicted in bold 3 or 4 digit
- Underlined
- Adjacent to or under the “H” or “L”
- Abbreviated automated ship plots of wind direction
- 8 points on the compass rose
- wind speed
- In knots
- Present reported weather
- Using current standard symbols
The product of the surface charts:
- Issued in two ports which overlap by 10 degrees of longitude
- Both parts project low or high pressure system’s forecast position
- by drawing an arrow to the 24 hour position labeled as
- an X for lows and
- circles with an X in the middle for highs
- bold two digit millibar central pressure value underlined under or adjacent to the 24 hour position label
- by drawing an arrow to the 24 hour position labeled as
what inabled mariners to use surface analyses as a work chart?
- Surface analyses are doubled in size and issued as a two part product
- Mariners can use the appropriate part if operating only in that part of the ocean which will impact the vessel
- Mariners can then know how the weather system will impact their vessel
- Mariners can use the appropriate part if operating only in that part of the ocean which will impact the vessel
how to extend the usefulness of the surface charts (product)?
- Use with a 500 mb analysis
- The 24 h forecast position of synoptic scale weather system will help in determining the weather systems’s
- Motion and
- Intensity trends
- The 24 h forecast position of synoptic scale weather system will help in determining the weather systems’s
surface analysis is broadcasted…, this can…
- Less than 3 ½ hours from the valid synoptic time
- Substantially aid the independent decision making process for
- crew safety
- protection of the ship
- prevention of cargo damage
- maintaining schedules
define 500 mb chart
- constant pressure chart which means that everywhere on the chart the air pressure is the same (500mb)
- given in tens of meters above sea level
- 540 lines means that the 500mb is at a height of 5,400 m above sea level
500mb is on the height of:
- 5600 meters or
- Above18,000ft above sea level
: 500mb varies from place to place due to
- The density of the air column
heights increase when:
- The air is warmer and
- less dense
the distance between warmer air and colder air lines indicate:
- the slope of the 500mb surface
the closer the height contours on the 500mb chart the …
- faster the upper level wind flow
- the stronger the temperature contrasts
- more active is the surface weather below
- the stronger the temperature contrasts
the 500-mb chart depict:
- Height contours above the earth’s surface at 60 m intervals.
- Wind speeds of 30 knots and greater.
- short wave troughs (generally 50 degrees or less in longitude)
embedded within the 500-mb height field are the
- The short wave troughs (generally 50 degrees or less in longitude)
Embedded within the 500‐mb height field are the short wave troughs, generally 50 degrees or less in longitude. These are drawn on the charts as
- Bold dashed lines
short wave troughs will assist the mariners in
- Locating surface low pressure systems
- Developing lows on frontal waves
The development and strengthening of surface lows and the associated bad weather most often occurs on:
- The eastern side of 500mb troughs
The development and strengthening of surface highs and the associated good weather most often occurs on:
- The western side of 500mb troughs
the 500-mb winds approximate:
- The speed of motion of surface extra‐tropical lows (often about 1/3 to ½ of the 500‐mb wind speed) and
- Surface wind force (approximately 50 percent), particularly in the colder SW quadrant.
On the marine version of the 500mb charts the “564” (5640 meter contour) is: (APEARANCE)
- Highlighted in dark black
On the marine version of the 500mb charts the “564” (5640 meter contour) is highlighted in dark black as it often depicts:
- The southern limit of force 7 (28‐33 kt) or higher surface westerlies during the winter and force 6 (22‐27 kt) surface westerlies during the summer.
This height contour is also widely used by the professional mariner for:
- general surface storm track direction – the primary surface low storm tracks will tend to lie about 300 to 600 nautical miles northward of this line.
can 500-mb products be used alone? If not what should you use them with?
- The 500‐mb products are not intended to be used alone. They are to be used along with the surface charts.
what are the prognostic charts
- The 6, 24, 36, 48, 96 hr forecasts are generated twice a day for 00 and 12Z
- They depict synoptic scale flow:
- patterns
- location
- amplitude
of long and short waves
what should you use to determine the movement and trends of the upper air pattern?
- Prognostic charts synoptic scale features compared with previous analysis
prognostic charts can be used with:
- Surface analyses,
- sea state analyses, and
- meteorological satellite imagery,
which are valid at the same synoptic time.
Tropical Cyclone Forecast/Advisory is issued when
- meteorological data indicates that a tropical (or subtropical) cyclone has formed
Special advisories or forecast are issued whenever
- unanticipated significant changes occur
tropical depression stage
- maximum sustained winds of 34 kt (38 mph/61 km/h) or less
Once a system develops to the tropical depression stage (maximum sustained winds of 34 kt (38 mph/61 km/h) or less) this product is issued every
- six hours
- until the cyclone either becomes extra‐tropical or weakens to below tropical depression status.
components of advisory message:
- the title of the product and the office of origination
- time and date of issue
- the date/time and location (tenth of a degree) of the center of the storm
- direction (to the nearest 5 degrees) and speed (in knots) of the storm’s forward motion.
- Current location information includes:
- An estimate of the lowest atmospheric air pressure.
- Diameter of the storm’s eye.
- Maximum sustained wind speed along with the maximum speed of gusts.
- Radii of the maximum wind in four quadrants (NE, SE,SW and NW) in three categories; ≥64 kt, ≥50 kt, ≥34 kt.
- Also, the extent in each quadrant of seas at least 12 feet high is provided, if any
- The forecast will contain 12, 24, 36, 48, 72, 96, and 120‐hour tropical cyclone forecast positions and wind radii. Due to forecast uncertainties, at 48 and 72‐hour forecasts the radii for the 64 kt winds are not provided.
Under an international scheme prepared by the WMO, practically all ocean areas are today covered by
- radio weather bulletins for shipping on the high seas
The bulletins are presented in a more or less standard form so that they are easily understood:
- The text being in the language of the issuing country and English.
- In a few cases a simple code may be used.
- These bulletins are designed to give the maximum of essential information as briefly as possible
- In some cases more than one nation issues bulletins for the same area: if these bulletins give a similar forecast the mariner can have more confidence in it.
Many of the larger oceans are subdivided into sections to facilitate
- Descriptions of the actual and forecast weather.
Most bulletins for the high seas and some for coastal areas contain reports of
- existing weather conditions at a selection of ships and/or shore stations
Most bulletins for the high seas and some for coastal areas contain reports of existing weather conditions at a selection of ships and/or shore stations. These reports include:
- these data are included to give the marine an overall picture of the situation in as wide an area as practical
- wind direction and
- force,
- weather,
- visibility,
- barometric pressure and,
- sometimes, wave data from the ships
ships require
timely and accurate presentation of meteorological and
oceanographic information for a large geographical area to plan for safe and
economical operations.
Ships require timely and accurate presentation of meteorological and
oceanographic information for a large geographical area to plan for safe and
economical operations. This information is most user friendly when presented in
graphic form
HF Radiofacsimile is recognized as
he most
widely used medium by ships for receipt of
graphically displayed environmental analyses
and forecasts
Radiofacsimile, also known as
Radiofax, HF
FAX, or Weatherfax
Radiofacsimile, also known as Radiofax, HF FAX, or Weatherfax, is a
means of broadcasting graphic weather maps and other graphic images via HF (shorter wavelengths) radio
Maps are received using a
dedicated radiofax receiver connected to an external facsimile recorder or PC equipped with a radiofax interface and application software.
Three primary types of products are issued
upper air 500 mb charts
• surface pressure and
• sea state charts
Additional charts include sea surface temperatures (SST), tropical streamline and
surface analyses, and meteorological satellite imagery.
The sea state analysis is prepared for
each ocean at the time of day when the greatest quantity of observations are taken
The sea state analysis has ………….. contour intervals
solid 1 meter
The sea state analysis has solid 1 meter contour intervals.
• Where appropriate,
relative maxima and minima combined wave height values (approximately 1/3 the height of the wind wave added to the height of the swell wave) are centrally depicted and inside a box under or adjacent to the wave height value.
……………………………. are used for guidance in areas of sparse data and are used to verify model guidance.
To produce the final analysis ships and buoys reporting data along with the NCEP significant wave forecast models
The sea state analyses highlight where
the most significant combined sea states prevail. Dominant wave direction arrows are also depicted.
When viewed together with the surface analyses, the user should have a
complete picture of surface weather conditions in a very timely manner, thus substantially aiding the mariner in crew safety and the protection of property.
