whatsnew updates for v3.13.0rc0 (#6583)

* whatsnew updates for v3.13.0rc0

* fix whatsnew entry

Author: bjlittle

docs/src/whatsnew/latest.rst renamed to docs/src/whatsnew/3.13.rst

@@ -1,21 +1,43 @@
 .. include:: ../common_links.inc
 
-|iris_version| |build_date| [unreleased]
-****************************************
+v3.13 (24 Jul 2025 [release candidate])
+***************************************
 
 This document explains the changes made to Iris for this release
 (:doc:`View all changes <index>`.)
 
 
-.. dropdown:: |iris_version| Release Highlights
+.. dropdown:: v3.13 Release Highlights
    :color: primary
    :icon: info
    :animate: fade-in
    :open:
 
-   The highlights for this major/minor release of Iris include:
+   The highlights for this minor release of Iris include:
 
-   * N/A
+   * Extended :data:`iris.loading.LOAD_PROBLEMS` to all NetCDF objects added
+     to a :class:`~iris.cube.Cube` during loading, thus providing richer
+     diagnostics to help understand loading issues.
+
+   * Added support for loading and saving multiple *Coordinate Reference
+     Systems* (CRS) for a :class:`~iris.cube.Cube` when using NetCDF.
+     Additionally, we can now generate a *Well-Known Text* (`WKT`_)
+     representation of the CRS when saving, which can be useful for
+     interoperability with other tools.
+
+   * Made :class:`~iris.MeshCoord` immutable, with automatic updates when the
+     associated mesh changes.
+
+   * Enabled correct loading and saving of bounds for
+     `CF Parametric Vertical Coordinates`_.
+
+   * In terms of performance, we have made significant improvements to the
+     memory usage of hybrid coordinates, which are now automatically rechunked
+     to avoid excessive memory usage. This is particularly useful for large
+     datasets with derived coordinates, and reference surfaces are now lazy by
+     default. Additionally, we've extended NetCDF compression to include
+     auxiliary coordinates and ancillary variables, which can help reduce file
+     sizes and improve loading times 🚀
 
    And finally, get in touch with us on :issue:`GitHub<new/choose>` if you have
    any issues or feature requests for improving Iris. Enjoy!
@@ -65,7 +87,7 @@ This document explains the changes made to Iris for this release
    See `CRS Grid Mappings and Projections`_ for more information.
    (:issue:`3388`:, :pull:`6536`:)
 
-#. `@ESadek-MO`_ made MeshCoords immutable. :class:`iris.MeshCoord`s are now updated automatically when
+#. `@ESadek-MO`_ made :class:`~iris.MeshCoord`\s immutable. :class:`iris.MeshCoord`\s are now updated automatically when
    changing the attached mesh. All changes to the :class:`iris.MeshCoord` should instead be done to
    the relevant :class:`iris.Coord` located on the attached :class:`iris.MeshXY`. This change also affects 
    the behaviour when calling :attr:`iris.MeshCoord.points` and :attr:`MeshCoord.bounds`, which will return
@@ -84,17 +106,17 @@ This document explains the changes made to Iris for this release
    to also include any auxiliary coordinates and ancillary variables with the same ``shape``.
    (:issue:`6539`, :pull:`6552`)
 
-#. `@pp-mo`_ added support for saving and loading the special ``GRIB_PARAM`` attributes to netcdf, as used
+#. `@pp-mo`_ added support for saving and loading the special ``GRIB_PARAM`` attributes to NetCDF, as used
    by iris-grib to record the exact grib-file encoding of phenomenon types.  This means that data sourced
-   from GRIB grib files can be freely saved and re-loaded to netcdf without loss of information.
+   from GRIB grib files can be freely saved and re-loaded to NetCDF without loss of information.
    (`Issue Iris-grib#596 <https://github.com/SciTools/iris-grib/issues/596>`__, :pull:`6566`).
 
 
 🐛 Bugs Fixed
 =============
 
 #. `@HGWright`_ added a new warning to inform users that the boolean coordinate generated by
-   :meth:`iris.coord_categorisation.add_season_membership` is not saveable to netcdf. (:pull:`6305`)
+   :meth:`iris.coord_categorisation.add_season_membership` is not saveable to NetCDF. (:pull:`6305`)
 
 #. `@bouweandela`_ changed the ``convert_units`` method on cubes and coordinates
    so it also converts the values of the attributes ``"actual_range"``,
@@ -106,7 +128,7 @@ This document explains the changes made to Iris for this release
 #. `@stephenworsley`_ fixed the html representation of cubes in Jupyter when coordinates
    share the same name. (:pull:`6476`)
 
-#. `@schlunma`_ fixed loading of netCDF files with coordinates that have
+#. `@schlunma`_ fixed loading of NetCDF files with coordinates that have
    non-string units. (:issue:`6505`, :pull:`6506`)
 
 #. `@ukmo-ccbunney`_ correctly set the ``bplon`` PP field parameter when saving
@@ -191,7 +213,7 @@ This document explains the changes made to Iris for this release
    (:issue:`2985`, :pull:`6562`)
 
 #. `@pp-mo`_ made a unified mechanism for 'managed' cube attributes: ones which get
-   converted between an iris-internal and an in-file form for saving/loading to netcdf,
+   converted between an iris-internal and an in-file form for saving/loading to NetCDF,
    such as STASH objects in a STASH attribute.
    (:pull:`6566`).
 
@@ -210,3 +232,5 @@ This document explains the changes made to Iris for this release
 .. _CRS Grid Mappings and Projections: https://cfconventions.org/Data/cf-conventions/cf-conventions-1.12/cf-conventions.html#grid-mappings-and-projections
 .. _Ncdata: https://github.com/pp-mo/ncdata
 .. _Trusted Publishing: https://docs.pypi.org/trusted-publishers/
+.. _WKT: https://www.ogc.org/standards/wkt-crs/
+.. _CF Parametric Vertical Coordinates: https://cfconventions.org/Data/cf-conventions/cf-conventions-1.12/cf-conventions.html#parametric-vertical-coordinates

docs/src/whatsnew/index.rst

@@ -6,13 +6,13 @@
 What's New in Iris
 ------------------
 
-.. include:: latest.rst
+.. include:: 3.13.rst
 
 .. toctree::
    :maxdepth: 1
    :hidden:
 
-   latest.rst
+   3.13.rst
    3.12.rst
    3.11.rst
    3.10.rst