Re: PredictWind Presentation - and some extra info on GRIB files


David Vogel
 

Hi there Teun,

With regards to: " Weather4D allows me to easily run and re-run various routing scenarios whilst underway, without needing to go online each time, as is the case with the PW Offshore app"

Question: > where & how does Weather4D gets it updates if the iPad is not connected to the internet or satellite?

Answer: Wx4D does not get any updated GRIBs unless connected to internet (or polling GRIBs via SailDOCs). The various routing scenarios I am referring to here are exploratory boat-scenarios.

To explain, whilst underway I download the GRIB/s once a cycle (normally daily under routine circumstances, but 12-hourly under dynamic weather conditions or when decisions need to be made). With a valid GRIB loaded, you can adjust various parameters in Wx4D, such as setting different routes, RTE start-end & intermediate waypoints, ETD, or different polars, or adjust the polar weighting; then re-run the scenario locally. Calculating each run takes about 10 seconds. You can then compare the result of each scenario-set visually on-screen. For example, what is the effect of a polar set at 85%, versus 45%, or going great-circle PresentPosition-to-Destination versus via x, y or z. You can see the estimated future position of the boat with respect to the weather systems and wind/wave fields for each of the different selected scenarios (fast, slow, left, right). This all happens locally.

Whereas with PW, the routing calculation for a single route (using different WX models) takes place online, with the results being downloaded to the Offshore app. Meaning, with PW, you need to go online to do each a new routing calculation (scenario analysis, WPT, polar setting), even within the same forecast period. And you cannot hold-over to see the results of a previous run.

Does this answer your question? Feel free to ask if any further explanation is required.

In any event, hoping to catch up if we can get back down to Hope Island marina before we wing it back to NZ. Happy to show you then.

Best,

David


From: <main@AmelYachtOwners.groups.io> on behalf of Teun BAAS <teun@...>
Reply to: <main@AmelYachtOwners.groups.io>
Date: Sunday, 19 June 2022 at 8:30 am
To: "main@AmelYachtOwners.groups.io" <main@AmelYachtOwners.groups.io>
Subject: Re: [AmelYachtOwners] PredictWind Presentation - and some extra info on GRIB files

Morning David,

When using Weather4D on an iPad during passage (see yellow highlighted section below) where & how does Weather4D gets it updates if the iPad is not connected to the internet or satellite?

Best Regards Teun
SV AMELIT  A54  #128

HOPE ISLAND MARINA (near BRISBANE) QLD AUSTRALIA
June 19, 2022 08:30:18

You can follow AMELIT via this link: https://forecast.predictwind.com/tracking/display/AMELIT

-----Original Message-----
From: main@AmelYachtOwners.groups.io <main@AmelYachtOwners.groups.io> On Behalf Of David Vogel via groups.io
Sent: Sunday, June 19, 2022 07:52
To: main@AmelYachtOwners.groups.io
Subject: Re: [AmelYachtOwners] PredictWind Presentation - and some extra info on GRIB files

Good ZOOM hook-up - thank you Bill & Tilo for organising and moderating.

I learnt a few good things: use of high-resolution models for local forecasts; and the better speed of the PWoffshore APP because it caches data locally.

If you are like me, a little 'old school', preferring to access and study all kinds of weather information from diverse source, or for those interested in some more detail and background information about GRIB files, the attached Weather Compendium provides a general overview about how to obtain and use GRIB files, and other sources of weather data, albeit with a focus on French Polynesia.  See section 32.

As background, I have been using PredictWind on and off for 8 years - as only one of the many tools in my weather toolbox - and trialled the PW PROFESSIONAL level of subscription for our recent trip Fiji-NZ, during which we encountered some gnarly weather.  The responsiveness and level of support from the PW team is second to none.

That said, as a weather 'geek', I still prefer to run my own weather forecasting and routing tools, and my "Go To" tool is Weather4D on an iPad, which I have also been using for passage-making since 2014 without complaint.  Weather4D allows me to easily run and re-run various routing scenarios whilst underway, without needing to go online each time, as is the case with the PW Offshore app.  There are a number of other apps and PC/Mac applications that do the same thing.  But for many cruising types, increasingly PW is a fully capable and functional tool for visualising key elements of the weather forecast.

I hope the attached is of some interest.

David
SM#396, Perigee

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