warmth of shelter is more comforting on land and the life there is more social, less lonely than the life of a seafarer. 

Beginning on line 11, the Seafarer notes how the waves leave him continually drenched. This makes the cold air even more unbearable: 

pierc'd with cold

were my feet, 

bound with frost, 

with cold bonds. (16-19) 

The Seafarer continues with more references to the cold weather in subsequent lines. But first he notes that men who live comfortably on land do not have any idea how miserable and sad his life as a seafarer has been. His descriptions of his loneliness are usually coupled with images of coldness. His line of being miserable and sad is followed by "on the ice-cold sea / a winter pass'd, / with exile traces; / of dear kindred bereft, / hung o'er with icicles." These are lines 28-31 of the first part/stanza and line 1 of Part 2. 

Different translations of the poem show it divided in different ways. Some have it in two or three parts with no separation of stanzas. Some have it as one continual poem. And some divide the poem into stanzas of four to five lines. So, it's not clear what the first "stanza" is, but many of the translations have a first "section" and this seems to be between 15-30 of the first lines. 

In the Anglo-Saxon poem "The Seafarer," images of weather abound.

The first example describes the water. We can infer that the weather is harsh because of the manner in which the water moves, causing him pain:

It [the poem] tells

How the sea took me, swept me back

And forth in sorrow and fear and pain...

Immediately the unknown author describes again the way storms have crashed around him:

It tells

Of smashing surf when I sweated in the cold

Of an anxious watch, perched in the bow

As it dashed under cliffs.

The words that describe the weather are "smashing surf" and "dashed under cliffs." If the weather had been fair, the ocean would be calm.

In the following lines, the reader learns that the sailor is traveling in wintry weather:

My feet were cast

In icy bands, bound with frost...

Note the use of the words "icy" and "frost."

The author continues to describe the weather, worse than it was before:

On an ice-cold sea, whirled in sorrow,

Alone in a world blown clear of love,

Hung with icicles. The hailstorms flew.

The only sound was the roaring sea,

The freezing waves.

The images of the harsh weather are found in "ice-cold sea," "Hung with icicles," "hailstorms," and "freezing waves." Again, in order to experience these things, the weather must be wintry.

The poem is a mariner's story of the many long and lonely years he has spent sailing to "a thousand ports." In his profession he has, understandably, been exposed to all kinds of weather. However, the beginning of the poem seems to concentrate on the cold, perhaps a parallel to the sense of isolation he is experiencing. There is little to warm his heart beyond the sound of the birds. He feels desperate about his separation from society and even from the land. He is "Alone in a world blown clear of love." At the same time, he recognizes that he is the kind of person who could have no other life, for he is a sailor at heart.

While the descriptions of weather provide images of the difficult circumstances under which the seafarer sails, they also provide the reader with a glimpse of the man's heart and soul as he is irresistibly drawn to the water, even while he also misses the pleasures of friends and a stationary life—things he realizes he can never have.

In the first stanza, the seafarer presents images of the hardships he has suffered at sea. He describes "smashing surf when I sweated in the cold / Of an anxious watch, perched in the bow." In this image, the surf is pounding against the boat in which the seafarer is traveling in the bow; he anxiously watches the waves. He is so cold that he is covered with condensation, perhaps ice. Later in the first stanza, he says that he felt a sense of wretchedness as he drifted "On an ice-cold sea, whirled in sorrow / Alone in a world blown clear of love, / Hung with icicles." In this image, the sea is frozen, and the world is covered with ice. The seafarer then describes a storm in which "the hailstorms flew. / The only sound was the roaring sea, / The freezing waves." Hail descends on him, and all he can hear is the roaring of the sea and the waves. With these vivid images of a frozen world, the seafarer describes himself as completely alone, wretched at heart, and utterly at the mercy of the whims of nature in northern climes. 

The Anglo-Saxon or Old English poem "The Seafarer," from the Exeter Book, was most likely written in the early 10thC. sometime between 925CE and 950CE.  It's most important distinction is that it is the first Old English poem we have that deals solely with the hardships of a  sea-faring life.

Imagery of weather and suffering from the cold at sea abound but not in the first stanza (as we usually divide the poem into stanzas).  Several translations into Modern English divide the poem differently from the original in order to make the poem read more smoothly and coherently in Modern English, but I will discuss the weather imagery as it appears in the poem's original configuration.

In the second stanza, for example, the seafarer, in his "true song" about the hardships he has suffered, refers to

many worries [cearselda fela]/the terrible tossing of the waves [atol ytha gewealc] 

Fettered by cold were my feet/bound by frost in cold clasps

As he does throughout the poem, the seafarer describes the essentially hostile environment of life at sea.  In this case, he uses metaphorical language to compare the cold and frost to (probably) iron clasps that bind his feet.

The seafarer continues the harsh imagery of life at sea in the third stanza when he tells us that

how I, wretched and sorrowful, on the ice-cold sea/. . .hung about with icicles; hail flew in showers. . . [and he heard nothing but] the roaring sea, the ice-cold wave.

In this stanza, he also describes himself as "in the paths of exile, bereft of friendly kinsman," an important statement because it tells us that he is not on a voyage of discovery with other men familiar to him but that he has, for whatever reason, left his homeland and embarked on a lonely voyage.

The importance of the seafarer's description of the harshness of the weather is to remind the reader that life itself can be harsh and lonely and that, ultimately, peace can be found in the "eternal blessedness" in the afterlife.

The original Anglo-Saxon isn't broken into stanzas, but some translators break the text into stanzas of ten lines each, while at least one other translator renders the poem as prose paragraphs, with the first break at line 27. Images of isolation in lines one to ten are those of a man's isolated internal struggles: isolated (and isolating) "anxiety at heart"; lonely, isolated "hazardous night-watch"; isolated hunger and weariness of mind as "[h]unger within tore." One image speaks of geographical isolation during years at sea, "[w]ave tossed," bounded "by cliff-wall." [The ~ below indicates a caesura break, which some translators turn into a line break (e.g., line 5 in the Anglo-Saxon with caesura is this: "gecunnad in ceole     cearselda fela,").]

Bitter the breast-care ~ That I suffered,
Known at my keel ~  Many a care’s hold, ...  5
When wary night-watch ~ Found me often
There at the ship’s stem, ~ Wave-tossed, by cliff-wall. ...
Hunger within tore ~ The sea-weary soul. ....

Images of isolation in lines one to ten show (1) the isolation of anguished psychological and mental suffering, along with (2) the isolation of hazardous night-time duty on a ship in a dangerous sea in (3) an isolated and violent physical geography. Images of isolation in the first ten lines are few, because the seafarer's hardship at sea may be suffered in company with a whole crew until we know that he is alone and isolated on shipboard, which he tells us at lines 15 and 16:

Weathered winter ~ In ways of exile, 15
Bereft of my brethren, ~ Hung with ice-shards;

That his true isolation is withheld until lines 15 and 16 renders the discovery more heart-wrenching and meaningful because, until then, we harbor a questioning hope that he is not alone in the horrible seas he has been battling. Images of isolation after line 16 are more plentiful. For example, he hears no sound, including that of a human voice, "I heard nothing but the raging of the sea." For the seafarer, shared human entertainment (like a sailor's song and jig), shared human laughter and shared "mead-drinking" are replaced by the swan's song, the gannet's cry, the curlew's call and the sea-mew's singing:

There I heard nothing but the raging of the sea, the ice-cold wave. Sometimes I would take the song of the swan as my entertainment, the cry of the gannet and the call of the curlew in place of human laughter, the sea-mew's singing in place of the mead-drinking. (S.A.J. Bradley prose translation)

These images paint the picture of an isolation from human contact that is absolute. Only birds enter to share and soften his bleak, lonely existence.

There I heard naught ~ But sea roaring,
Ice-cold wave. ~ Whiles the swan’s song
Had I for pleasure; ~ Gannet’s clamour,  20
Curlew’s crying, ~ For men’s laughter;
The mew’s singing ~ For mead-drinking. ...
Sea-foam-feathered; ~ No bright companion
There to comfort ~ The careworn soul.

In the first selection, the narrator is portrayed as a prisoner in his surroundings, alone in his personal and icy dungeon. 

My feet were cast
In icy bands, bound with frost,

In the second example, the image is of the narrator beset upon by storms, having no shelter from the dangerous conditions and no one to protect him from them.

How wretched I was, drifting through winter
On an ice-cold sea, whirled in sorrow,
Alone in a world blown clear of love,
Hung with icicles. The hailstorms flew.
The only sound was the roaring sea,
The freezing waves.

In this last image, readers see the narrator as surrounded only by rocky cliffs, with the screams of birds as his only company.

Storms beat on the rocky cliffs and were echoed
By icy-feathered terns and the eagle's screams;
No kinsman could offer comfort there,
To a soul left drowning in desolation.

The poet uses the weather, the cries of birds, and the unwelcoming rocky cliffs to portray the alienation felt by the Seafarer.